The timing mechanism is worn out ................ Hmmmmm
And did he try to sell you a new one by some chance?
OK, parts are available for the Mdl 15s. What series is it? 15-90, 15-91 ????????
You just have to look for them. There is no such thing as unfixable, only a salesman who don't want to fix it.
If I can bring a rusted up 99K back to life a real repairman can fix a 15.
Joe