who do i trust for service?

Dennis Baker reseals old vintage guns.

Baker Airguns

Check Crosman 600 on eBay....there was a guy posting that service. I've reseal a couple myself with good results. Kinda trick disassembly, but it can be done with one simple home made tool.

Crosman?

Contact Tim McMurray at Mac1 Airguns. He's been rebuilding Crosman 600 pistols for a very long time.

.....see below... 

If you want it souped up a little bit ,Tim McMurray is the go to guy.

Baker airguns

mac1....may take a few weeks longer, but the work he does and the higher quality parts he uses are the best in the biz for american airguns.. i get my benjamin and sheridan parts from there many times... i fix a lot of those for folks around here local face-to-face in my home if posssible (i pickup and deliver for some elders here, too)....... -- secondly , i use precision pellet in penn for older crosmans, too. my model 160 shot 660-670 fps for over 30 shots - and he installed a scoperail on it for me he's cheap and fast turn around. he's pretty good too, tho... i get old timey benjamin parts there.. - cheers.. i hope that helps. - paul.

They are not super hard to get apart, just need to pay attention. I rebuilt one a few years back. The hardest part was getting it apart. The inner cylinder tube had varnished itself to the outside tube of the frame. Spent two weeks with Kroil every night to finally get it broke free and apart. Along with a few helpful taps with a hammer and block of wood. The o-rings are usually the problem. mine worked fine for a while until I let it sit for a while. next time I used it I forgot to cock it before charging, and now it won't hold CO2 again. Well, need to rebuild it in my spare time.

Good luck with yours, 

You can add Roy @ mountain air airguns to the list.