transmission pops out of 3rd..

[moloc325]

ok so i have a question...i have a 87 325e..when i up shift into third and let off the clutch my transmission pops out of gear...so i have to push it back and very slowly let off the clutch praying it stays in...i have no idea why...i dont recall mis-shifting or anything. it doesnt happen when i downshift..only upshifting....anybody have any suggestions onwhat it could be...would i be better having it looked at or just getting a used tranny cheap?
thanks
chad.

[AndrewBird]

Have you checked the fluid? You might want to drain it and see if there are any metal shavings or broken pieces of teeth in the fluid. Sounds like the 3rd gear syncro is dead/going out.