Single Pump Pneumatic Repair Question

I have a Feinwerkbau 601 10M target rifle that's almost 30 years old and it no longer holds air and needs its seals replaced.

Is this a do-it-yourself job? If so, where can I get replacement seals and instructions for replacing them?

If it's not a DIY job, is there anyone still servicing these rifles? Links and/or phone numbers would be appreciated!

Thanks!