I've only done a few sump replacements. 1275 Midget has a cork gasket. Gluing it to the sump pan with red gasket goo did a great job there. The trick was to be very careful to not over tighten the bolts. It had to come off again because there was a bearing shell problem. But the oil pan was easy peasy.
Montego diesel - the oil drain plug fitting spun loose due to poor brazing at the factory. I got that off by drilling a hole in the sump and leaving it to drip overnight. But the exhaust had to come off so a proper Pain-in-the-bits. The fitting and drilled hole were silver soldered as my gas torch was not big enough for braze. A splash of black paint after it had been refitted and job done.
It went back with silicone RTV applied to the sump pan. It had to be done quickly because despite wiping inside the crankcase it just never stopped dribbling oil. Anaerobic sealants probably did not exist black then but are not really suitable for a pressed seal oil pan and no gasket.
Panda, same as above - folded tin to casting. RTV is the best option.
I've not done a Panda 100 HP oil pan. You might get away with exhaust in place but as its cast alloy to cast alloy, Loctite 518 will be ideal. While you are in there, drill the edge of the exhaust support bracket bolt at 120 degree intervals. It's another "drilled right though" jobbie that will tear the threads if the ring of aluminium oxide is not broken off the bolt threads.
