I haven't read this entire thread yet, so maybe someone else has already thought of this, but if not:
1 problem with buying a second hand compressor that was initially intended for paintball is that paint ball stores don't understand the issues with breathing quality air. SO! If they didn't use the proper synthetic oil when doing maintenance on the compressor and instead used something NOT compatible with breathing air, then that compressor is junk for scuba diving.
Is there any way you can KNOW for sure that they only used breathing quality lubricant? If not, you need pass on that compressor no matter what the cost.
Using quality mineral oil does not make the compressor junk for breathing air. After all not too long ago all the compressors used mineral oil for breathing air, and many shop compressors still do.
Synthetic oil is better in the use, lasts longer between changes and has a higher flash point over mineral oil, but both can be used. If I were to buy a second hand compressor I will have it pulled down and serviced and then lubricated with synthetic oil only, however unless the compressor went for a bargain price, it would probably not be worth doing that.
---------- Post added February 24th, 2015 at 12:04 PM ----------
Just checked my Drager/bauer compressor PE-100-T, PE-100-T. The filter fitted is a 057679-410 (same as yours) with 68 gm molecular sieve and also activated carbon. If you look up the bauer specs for your compressor and the manual it should show the tower filter air path. This might explain any differences as well. My manual is
http://wssproducts.wilhelmsen.com/mediabank/store/2552/PE-100-T-0110GB.pdf and in it you can see the air enters the base of the tower, where there is the final condensate drain. The air then goes up the filter body on the outside, over the top and then down into the filter body (thus trapping more moisture in the base of the tower), and then I suspect once it passes through the medium there is an internal pipe in the filter body that take the clean air out through the top of the tower.
Now this might be a change from previous models where the air entered the base of the tower then straight up the cartridge through the medium. I suspect an attempt to make the cartridges to last a little longer.
Your tower looks different in that it takes the air out the base, however there may be internal piping. I suspect the difference is the filter tower and how the air is routed. Another option is to add an additional filter after the tower as I have, ensuring though that you also add another priority valve to maintain 100 BAR or so in the second filter body.
Or if its all too much, just buy another bauer so you then know its ok.