We've had good success by letting the engine sit as long as possible for the oil to drain down.
remove 1 bolt at a time.
brake clean the bolt and block threads
Use a small amount of permatex Ultra Black on the bolt threads and if possible the block as well. ( wooden stick Q-tips work well)
Reinstall
Move onto the next bolt until all the leakers are done. Do not overtighten when reinstalling as the gaskets may not like it