That was my plan with the magnet. I bought all new billet servos and accumulator piston too.
Just a point of interest:
When I first bought my car and drove it home it shifted directly from first to third.
I noticed it right away obviously when I test drove the car, and when I got it home I pulled the pan and adjusted the bands.
I thought it might have dropped the strut or had broken the band.
Fluid looked good and there were normal wear leftovers in the pan. (kind of like yours had)
The front band adjustment was so loose the servo pin for the band couldn't travel far enough to apply the band.
This caused the 1-3 shift and as soon as the bands were correctly adjusted second gear was back and it ran well for years afterwards.
It finally lost the front planetary gear set (I heard it coming for a few weeks) and I found that I could get a different trans for what it was going to cost to fix and shift kit the A904 so I replaced it with an A500 Overdrive and couldn't be happier.
$125 for the guaranteed trans, matching lockup converter and rear yoke.
$110 for a stage 2 Transgo shift kit, modded the crossmember and shortened the driveline.
The car runs at 2,100 RPMs at 75-80 and gets 25 mpg on the hiway with a mild built 400hp Magnum motor.
Might be an option for you, instead of putting money into a standard 3 speed.
The A500 (42RH) is the lighter version like a 904, but it seems to be doing really well.
If you wanted something heavier you could go with the A518 (46RH)
Neither of the "H" models needs a computer to run them as they are both hydraulic controlled transmissions, although there are some really nice aftermarket computerized controllers available.
