What can you use for crack pan or leak at the rivets
It depends upon how bad the crack or leak is. Most T pans were brazed around the arms and rivets. If the brazing has cracked, it can probably be re-brazed. If the arms are cracked, they need to be welded and reinforced, there are good ways and bad ways to do that. If the pan itself is cracked, it again depends upon where and how bad the crack is. Maybe welded. Maybe brazed. Maybe or maybe not reinforced.
Very important. Any heat enough to weld or braze can warp or distort the pan. It needs to be checked to make sure it is straight afterwards or it can result in a broken crankshaft.
Also, are you looking to repair it in the car under the engine? Or out in the open? Pan repairs should be done out in the open most of the time. Minor repairs can be done in the car, sometimes. Sometimes, a temporary patch can be done by thorough cleaning and J B Weld. Generally, all it can do is slow the leak down for awhile till you go ahead and fix it right.
Photos would help!
Drive carefully, and Merry Christmas! W2