There is a stripdown in the "idiots guide" sticky at the top of the page. http://www.airgunbbs.com/showthread....a-618-stripped. You may find this link helpful as well http://anotherairgunblog.blogspot.co...l/slavia%20618
Someone will be along to put up the link of how to make leather piston washers soon I expect. I think some of the piston washers were riveted and some had a screw to hold the washer.
If the front stock screws have sheared( broken off), you should be able to either wind them through or put a small drill through and retap to the correct thread. guessing 4mm? If the threads are stripped in the hole, then you can drill and tap them bigger and then use threadlock to put an insert in and drill and tap that to the right size.
The triggers are a bit crap on these and a new mainspring might result in it not cocking and holding. You could always get the trigger built up with weld