I have had the trans apart (and back together successfully for a couple years now!) on my 98 with an LT-1. I did not have to replace the output shaft seal. Good thing, because the nut that holds the flange onto the output shaft of a ZF Hurth is a VERY unique design. That means you would need the VERY special socket to remove it.
If I were you, unbolt the drive shaft and take a look at what I am describing. If yours is the same design as mine you might to consider paying to have the repair done...
Need LT-1 parts?
OIL FILTER: Factory installed is a Penzoil P23, Afta market brands, AC Delco PF-454 and a Fram PH-13 or PH-30 will work.
SPARK PLUGS: AC Delco MR43LTS (gapped to .040")
FUEL FILTERS: AC Delco 25171391 (pump inlet side)
89058397 (pump outlet side)
IGNITION WIRES: Call Inboard Online @ (877) 327-7175 and order part numbers 556010A (odd bank) and 556010B (even bank)