Where can I buy a piston seal for my Beeman GT600 Airgun made in Spain.

SOURCE: need repair parts for a Beeman model 800 or 850 air pistol

The only Airgun repair shop I know of is in Minneapolis, MN.
B & B Supply 4501 Minnehaha Ave So. Minneapolis, MN
Website: http://www.b-bsupplyco.com/
Hope this helps, mark the Gunsmith
Please leave feedback, Thanks!

SOURCE: How do I install a main spring in a RWS 34 spring airgun

You actually need special mainspring compressor to accomplish this. HOWEVER I strongly recommend you do not attempt this yourself. These springs are under a lot of pressure and can put a world of hurt on you should you screw things up. I suggest you contact Pyramid AIr to see how much they would charge you to send back.

SOURCE: dismantling an airgun for shipment

Not sure why you would want to dismantle it. Send it like it is. You may be able to get a box from your local gun store to ship it in. BTW, you can ship long guns via USPS, will save you money that way.

SOURCE: How to fix my beeman qb78 co2 single shot airgun from leaking almost immediately after shooting it only a few times?

Hi.
Check this guy out archerairguns.info.
Before you strip down your rifle, try the oil treatment.
Oil seals dry out even from factory delivered guns. This guy runs you through the "fix".
Simple steps but you need to buy some Pellgun Treatment Oil.
It's only a small tube and this guy walks you through the steps.
They're really good guns and owners really love theirs.
Good luck.