rear main seal would require the gearbox to come out....
good time to change all the axel / gearbox seals as well.
clean and refresh the starter motor and electrical connections,
in case manual transmission, inspect the clutch cylinder, throw out bearing, clutch condition.
flywheel would need machining and re-torqueing, use loctite on the bolts.
if auto, replace trans fluid as well if time to change is near.
for rear main seal activities, its best to combine several activities together