Well, first we'll need some information about where the leaks are. If you're mechanically inclined, Toyota's technical publications are excellent and quite easy for even the novice to follow.
Here's an online version of the Toyota Service and Repair Manual for the '90 Supra (aka TSRM):
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/ The "Engine Mechanical" section should cover most of the possible problem areas.