Anyone had these symptoms with a 904?

Hey guys:

The 904 in my '68 SL6 Valiant is acting up. I've been into one of these already and am pretty familiar with how they work but I'd like to get some feedback to help me decide if I want to repair this original unit or find another one with part-throttle downshift, etc. Here's what's up:

Field-find car. Sat for who knows how long. Trans full, no leaks, fluid dull red, "kickdown rod" adjusted per FSM.

First dozen test miles shifted soft between 1-2, but on time. 2-3 normal and on time. Third day of driving had long, slushy 1-2 shift, then acted fine ever after with a nice firm 1-2 shift, on time.

Drove several ~50 mile road trips during week, things degraded. Began having an audible "shwuup" noise immediately before 1-2 shift, every time. When it is COLD, it will sometimes start in second, sometimes start in 1st and shift directly to third, sometimes will stay in 1st until it warms up, skip 2nd when it finally shifts, then shift normally.

When it is HOT, it randomly shifts 1-3, or it shifts 1-2-3 and stacks 2-3. Today it shifted once from 1-2 at about 4mph. Otherwise it shifts on time and feels good except for that noise at the 1-2 shift.

I haven't lost any gears, 1st, 2nd, and 3rd do not slip under heavy acceleration, reverse feels good and I have engine braking in manual low. All of this bad behavior is amplified when the transmission is cold, but it still possesses the capability to act strange when hot.

Your thoughts are appreciated.