1950s 1956 Hydramatic Trans Flush

[Dave CLC#16900]

Hi, off to visit my long term project/barn find/ "Howard's Eldorado" / or as I like to call her, "Bernadette".  The previous owner bought the car in Chandler, AZ in 1970 from a film company that was shooting a Western in Tucson.  He had the transmission rebuilt in 1978 and said it was never right.  Howard parked her in 1981 when reverse stopped working.  He started some disassembly of trim to repaint the car and stopped.  I bought in 1990 from a local man that bought it to flip it from Howard.

I rebuilt the fuel and brake system immediately and drove it a couple hundred miles.  Seemed to work ok for me except reverse was not good when hot and made grinding noises.

I then took a long break from working on it.  Had to change storage locations 3 years ago and got it running again.  Reverse is not working now, may be low on fluid.

Going to lift the car up for the first time in 20+ years and drop the trans pan.  Was considering putting a quart of lacquer thinner in the fluid to loosen up the crud first, running it on the stands with minimal load. Then draining all the fluid possible from the fluid coupling and pan. Is adding thinner a bad idea?

I have a spare '56 Eldorado transmission but condition unknown from my parts car.  That car was parked in the 70s due to severe rust issues living in Pennsylvania.  One point of getting under the car is to see if Bernadette has her original trans or not.  Howard thought it was original.  If it isn't matching I may just send the parts car's trans for a rebuild.

Thoughts?  Would be great to make some short drives in the car next week....and replace the passenger window, and install the rebuilt antennae, and......

Dave