I just did a very similar job to yours a few weeks ago. My 2 cents is to replace ALL seals. My rear main seal was leaking even though I didn't see a spot of oil on the flywheel or clutch. It was dripping down the back of the engine/tranny plate. My rubber boot was wet as well. Once you replace the front transmission seal (remember to lubricate the inner lip of the seal), transmission front cover gasket, and rear main seal, reinstall everything. I say this, because you don't want to go back and replace the old seals a few months later if they decide to leak. If you still get leakage near the boot, it is most likely the clutch slave (or hose, if it's old enough). Keep in mind, from my experience, brake/clutch fluid sometimes drys up as it is not as heavy as oil. Again, if the clutch slave is leaking, replace it, but it is also recommended that you replace the clutch master cylinder at the same time, as you don't want a new slave or MC putting too much pressure on an old unit. Also, there is another possibility of a rear main cap leak. There are four seals that slide into the block where the rear main seal's cap can be removed. I believe this must be done by removing the oil pan, which at the same time you can replace the oil pan gasket. Reference here: http://www.classiczcars.com/forums/showthread.php?37250-Rear-Main-cap-side-seals