[way]

Perhaps the slush is a clue? I presume if you're anything like me, that you could observe the speedometer jump up and down as the wheels occasionally lost traction? Maybe that spinning loosened something up, maybe knocked some sludge out somewhere? It might be a good idea to change the fluid now to get rid of it?

I have recently regained first gear after having lost it for months. I presume it's only temporary because I suspect it's just because the synchro has worked its way back into a position where I can shift again. The reason I mention this is that perhaps something similar was happening with you except that it was caused by sludge. I'm already double clutching to get into first so it's probably not not for much longer.

Just a thought though. I know Amsoil is kind of expensive.