Transmission Fluid Change - 89 Comp, PCM 40A Transmission, 1:1.23 Ratio

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What ATF Fluid should I be using? Can't find ATF type A fluid called out on the tag but I believe the replacement is Dex/Merc. Not 100% sure...

Also, I have a small leak, are there any concerns with adding a bar's stop leak type product to my transmission? I was considering using Bar's Super Transmission Fix product. It's a synthetic blend for all transmissions but not sure if it would be compatible with the Dex/Merc ATF... Transmission preforms great but drips a little into the bilge. I also hear some chattering in the transmission when I put it into gear (idle speed - chatter goes away at higher RPM) while it's warming up. Once everything is warm, I don't notice any chatter in gear, at idle speed...
89 supra Comp Transmission.jpg