I have installed the governor seal Honda# 91231-891-003 on my new HRN216 mover. It has the GCV 170 engine.
It fits, is the correct part.
It took me about 20 minutes total, I took my time. It's disappointing that Honda opted not to include it on the engine.
There was oil residue already (before the seal), after less than an hour of use.
The online videos were a big help, especially the one from Taryl Fixes All.
Thanks also to Scrubcadet10.