I have only filled a T-case from the top, I don't have a 5 speed, so I can't
really comment on the fill procedure on that, but make sure you drain the
right box, not the T-case if you are wanting to do the trans.
And now because you don't have a open fill plug you need to make sure you
add the right amount of GL4 (only) lube, the GL5 will eat at synchros from
what others have posted. If you can't find GL4, look for "yellow metal friendly"
gear lube and you should be ok.
We had a really good discussion on this topic (rounded fill plugs) on here not too
long ago, did you do a search for it? I remember there were some excellent ideas
on how to solve the rounded out plug issue
Wild