Congrats on snapping this up it's a bargain. The focus guys are snapping them up for AWD conversions just the box would fetch a couple of grand.
What kind of extreme clutch did it have? There's a few things that can cause premature clutch failure eg:master cylinder or the delay valve.
There's no gasket/sealant between the gearbox and angle gear apart from the sealss inside/around the sleeve, if there's oil around there it's probably a damaged seal. Not uncommon for there to be a bunch of reddish/rusty looking stuff from the sleeve wearing out.
The collar should stay on the gearbox and is an interference fit, shouldn't really need anything to "stick it on" there's a difference between the manual and auto collars…is your loose or something?