Saga continues

Ureka the '85 300 Turbo with 160k miles now shifts. Thanks to all for the advice.

I used the Trans-X product for about 30 miles then changed the fluid and filter (transmission pan clean) but no improvement.

Tried the Lucas Oil transmission fix product-very thick-used 2 quarts- and after about 100-150 miles the transmission shifts again.

Changed the fluid (and added a quart of Trans-X)-will likely change fluid and filter after another 200-300 miles.

My question is how long will this "fix" last and is there any advice out there on special care and feeding of the transmission beyond normal fluid/filter changes?

If the long term fix means transmission replacement, I would welcome anyone's suggestion on avoiding the Dealer's quote of $6700.

Thanks.