First off, if your Badger compressor had a tank, it should have worked just like your new Sparmax. That is, unless the pressure switch was faulty or there was a significant leak, which apparently was the case. Secondly, the Badger hose relies on a metal to metal seal. See the photo on this page. If there is a burr or scratch on either surface it will leak. A little bees wax can sometimes stop it. You shouldn't need Teflon tape.
The size of the tank absolutely makes a difference in how often the compressor runs.
It's too bad they don't give more feedback. There are several things that could cause your symptom. I think both the Patriot and the Revolution are good airbrushes. The Revolution does have finer fit and finish, but the Patriot is easier to care for.
Could you elaborate more on what you mean by broken down? The Patriot is a pretty tough airbrush, much more than the Revolution with its tiny screw in nozzle. Also, the inside of my Patriot bowl is shiny chrome. Did you use ammonia to clean yours?
The Paasche V is a nice airbrush if you like a side cup like your Aztek. It won't accept your old Aztek cups though. As Monty wrote, the 155 is my favorite. But, there are a lot of good airbrushes out there. I'd go with something a little sturdier than the Harbor Freight, although it does spray OK. The Paasche VL and Badger 175 are built like tanks. And, with choice of nozzles will give a wide range of spray patterns.
I have to disagree with Bill about the cleaning kit. I think it's meant for bigger spray guns. Fine interdental brushes and some paper towels work well for me.
If by center tube, you mean the needle bearing, do not try to remove it. It is pressed in and factory replaceable on the Patriot. And, don't force anything through it.
You don't really need to completely dismantle an airbrush to keep it clean. Just clean the parts that the paint touches. I don't like the commercial cleaning brushes. The bristles are too stiff. Fine interdental brushes from the drug store work better. You might want to have a look at this page.
The Patriot is about the easiest internal mix airbrush to clean that there is.
The right pressure is the one that works the best for you with your airbrush and paint. Some airbrushes need more than others. Bottom fed airbrushes generally need a little more than the gravity fed type. External mix airbrushes usually need more than internal mix. Thicker paint needs more to spray well. Detail work is usually easier with lower pressure than needed for general coverage. It doesn't matter what the gauge says if you adjust pressure to get the output you want. It could range from 8 to 40psi. Once you determine the sweet spot for you, the gauge makes a handy reference, whether you set it with trigger up or trigger down. For my Badger 155 with a 1/4oz. cup and paint thinned the way I like it, somewhere around 15psi works for me.
There is only one o-ring in the VL, and that's in the air valve. If it's the old style, it's part number A52. The new style air valve gets part number A53. Have a look at this diagram. There is a packing nut, but that's not likely to be your problem.
If you can spray OK with the #1 nozzle, but not the larger sizes, I think your compressor is tired. The seals do wear out.
A little air leak at airbrush joints is normal. It can usually be stopped with a little bees wax or Chapstick on the threads.
My guess is the dirty needles are a large part of your problem. Wet sanding is a last resort. Try cleaning them with lacquer thinner or acetone. Judging by the needles, the nozzles are also probably filthy. Soak them in acetone or lacquer thinner and swab with cotton on a whittled down toothpick. Hold them up to a light and look in the large end. You should see nothing but shiny metal. Match the nozzle to the head by comparing the size of the openings. Number 1 is the smallest and 5 the largest. Check the needles for burrs on the end and the nozzles for tiny cracks.
Don't let solvent get in the air valve. If you are getting air all the time, the air valve may be stuck open or the tiny o-ring inside damaged. If you take it apart, be careful not to lose the tiny components.
I don't know about the older Badgers, but the current models are just as solvent resistant as the Iwatas. The only seal that isn't is in the air valve. I clean my Badgers with lacquer thinner all the time. There's no question Iwatas are fine airbrushes. I just prefer the 155 for painting models, and it runs a little over $60.
I'll add my 2 cents. There are a lot of good airbrushes. My favorite for all around use is the Badger 155. Some people don't like it. What feels good to me may irritate you. And, different airbrushes do have different feels. Some put out a whisper of paint, and others can blast out a lot. The 155 and similar acting 175 seem like a good compromise to me. The HP-C mentioned is a beautiful airbrush. But, with its .3mm nozzle and gravity cup, it wouldn't be my choice for model cars. The small nozzle means you might have to thin more. And, I like the ability to attach a bottle and know I have plenty of paint for the job. But, obviously some modelers prefer it. You don't really need a fancy airbrush. The proof of that is the fine work you see by people using the simple 350 or Paasche H. A lot depends on learning to use the one you have. But, if you lust after something like a Harder & Steenbeck CR plus Infinity 2 in 1 with gold plating, go for it. It will certainly do the job.
"That wont work on my gravity feed. It leaks paint past the needle seat if I do."
I'm not sure what you mean by needle seat, Paul. If you mean the front end of the airbrush, yes, it can leak if you pull the needle back too far. Like I wrote, it's touchy. If you mean the internal needle seal, the seal is leaking and needs to be adjusted or replaced. But, this would be a problem even in normal use.
At any rate, it's probably better to develop trigger control rather than to depend on tricks like this. And, that just takes some practice.