With Gulbrandsen there is 2 types of player models.One is made with a glued together stack (all the internal valves and attached pnuematics are connected to this) and the other version is a screwed stack.The screwed stack of course is easier to undo and work on , but if you have a glued stack then its very difficult to get apart without damage.Gulbransen players are very good players and work on the minumin amount of vacuum required , hence there motto "Easy to play" showing a crawling baby pushing the pedals.
If you have never rebuilt a player before , a Gulbransen is a mid range model in regards to difficulty and issues ,the best thing to do is double check that every piece of tubing and pipe work is fully attached , and that the bellows are working correctly and sucking air out making a vacuum to operate the player.
The best book around to do repaires/rebuilds is a book by Arthuer blizt (Player servicing and repair's) its a larger style soft cover book with a wealth of imformation.
In regards to the Gulbrandsen company , back in there hey day if a customer had a faulty player (stack ) the serviceman would remove the stack and do a factory replacement , if the stack was a glued model it was just simply chucked into the factorys furnace and used as fuel , they didnt even try to open them up or repair them.Many rebuilders cringe at the thought of rebuilding a glued stack , as it has to been sawn apart and then the gap has to be compensated for when been reattached together.
Yours been a late model should be a screwed version but i cant be 100% sure.