Cracked Aluminum Oilpan - Repair or Replace?

If you have access to the break, you can raise the front end, drain the oil and have it welded on the car. Degrease as best you can but I would not begin welding if oil was seeping from the crack.

I had a aluminum motorcycle engine case repaired this way. The case was cracked in several places when the drive chain broke for a previous owner. The case was not disassembled and did not leak after the repair.