Shift-shaft oil seal

When is the best time to install this seal? I removed the gear-case to replace the gasket and small O-ring on the clutch adjustment bolt. I replaced the clutch-release seal, but not the shift-shaft seal.

Should it go in after the bevel gear-case is installed on the engine, or before?
Thanks in advance.

This seal can be easily installed last, and have less risk for damage by waiting.

A small O-ring on the clutch adjustment screw/bolt also was changed-out, which is only accessible from inside...a perfect opportunity to do that.

Removing a 33 year old rock-hard paper-gasket is difficult, and requires diligent and careful-patient effort. Of course, 95% of it had to be stuck on the engine side. :evil:
Never again :S