The sloppiness is almost certainly due to shift bushings. At least in part.
The popping out of gear is more likely to be a problem with the internals of the transmission, specifically the dog-teeth and slider for 5th gear and the brake bands.
Dr. Evil has a DVD on 914 transmission rebuilding that can walk you through the process. It's a fairly thorough walk-through. We also have an article on the subject, written by "Red-Beard" back before the Doc started on 914 transmissions.
Pelican Technical Article: 901 Synchro Change
--DD