The 5 speed would enhance the Hiway driving, running along at 60-80 mph @ 3500/4000 rpm with bad sidepipes is painfull ! The 4 speed is fine for track and anything else.
Patrick, yes, the main suspect is rear main seal, but florescent
oil dye shows some other areas.
Don't know if my plan is compatable with "Bring a trailer"s format. quite a bit of Cobra action there as of late, bare alum csx 4000 went for $205 K last week.