The rear main seal is unto it's own - larger than the others. Your B21 doesn't have a rear camshaft seal like the B230's do. The seal housings will work loose, so if you do remove the flywheel check the bolts.
If the oil pressure light switch leaks it will produce oil that travels in a way to simulate a main seal leak. Check for that too, but if the flywheel is off you will easily see if the main seal is leaking.
Compared to most front drive cars the clutch job is very straightforward on your car. I did many over the years. Just be sure the engine tilts down enough, and to do that means releasing the flange nuts on the exhaust a few turns, as mentioned before. You might find it easier to remove and replace the uppermost bell housing bolt ( next one above the starter driver's side before lowering the engine. Put it in last.
Rhys