Changing 1990 crx dx automatic transmission fluid?

Bought a 1990 CRX DX today. It's an automatic with 127000 miles. Took it to the mechanic to replace the timing belt. They checked the car and everything was fine except that the transmission fluid "failed." They said they could service my transmission for $120!!!!!!! I know they're ripping me off and I can just do it myself, was just wondering what the best transmission fluid to use was and if I should put in any additives