I dug up a version of RMA 2.4.1 which is NOT compatible with zencart 1.3 and probably not 1.2*.

I attempted to fix it myself using winmerge, but it apparently has bigger problems than that. Maybe somebody with more knowledge would be interested in trying to help out.

Here are the original 2.4.1 files I believe I obtained from Merlin last year.
Download

Here are the updated winmerge files (admin/customers.php, admin/orders.php, include/functions/functions_general).

Download

Please help! :)