I think your B2 piston is hanging up. That whine sound is the brake band gradually stopping the clutch. I would almost guarantee that if it is not the B2 piston hanging up it is a worn B2 band. Beings that it did it for awhile then quit and now has came back that sounds just like the b2 piston hanging up. If it hangs up enough it will break and then it usually doesn't engage at all and you have no forward gears.

__________________
81 300SD daily driver/project
86 420SEL (sold)
85 380SE(in the graveyard)