Hello DS,
2001 Taco, awesome! Is it a 4cyl or 6cyl? It is common to replace the rear main seal for good measure, but if the rear oil seal is the gasket between the block and the main seal housing, then this is typically not changed unless it's leaking.
You can inspect the condition of the rear main seal by pressing your finger nail into the rubber. If it feels soft and its not leaking then I'd leave it. If its pretty hard (compare to pressing your nail into a cardboard box) then I'd replace it. Of course you could just replace it just to do it either way as they are not that expensive and you're (hopefully) unlikely to get in there for a while.
If you do replace it, then please do the following:
1) After you remove the old seal, take some medium grit sand paper and rough up the crank shaft at the contact area of the seal. This is important because after hundreds of hours of rotating inside the old seal, a smooth polished finish has formed on the crank shaft (this is what eventually leads to a leaking seal). Seals are made with a certain degree of tolerance but on the molecular level there are imperfections that must be worn in for the seal to fully seat & seal with it's mating component. If you simply slap in a new seal, the old polished finish won't be able to break the new seal in and it will end up leaking prematurely. The solution is to just add a few scuff marks to the crank shaft where you expect the crank shaft to make contact with the seal. Just rough up that old polished surface a bit. The new seal will thank you.
2) Before you install the new seal, add a bead of grease around the inner diameter of the seal. This will help the seal stay lubricated during the seal break-in period. Without this the seal may or may not run a bit warm. If it gets too warm then any surface imperfections may become glazed over thereby preventing the surfacing from breaking in properly.
The same applies with a clutch kit and is why it is advised to break-in the clutch disc in slowly:
1) The flywheel (and pressure plate) has been resurfaced with a semi-rough finish to remove the old polished surface and enable the flywheel to break the new disc in (same as #1 from above), and
2) The clutch disc is made from a fibrous material that has surface imperfections/ridges. If you overheat these ridges, they will glaze over (become cooked) and will require a much long time to wear down. If this happens, then you'll have a clutch kit that is only working via a reduced surface area along these glazed ridges (which ever ridges happened to be the tallest on a microscopic scale) and the new clutch kit will only be able to handle torque loads lower than expected (ie. once you cook it it will be easy to cook it again and again since it was never broken in properly to begin with) (same as #2 above).
The two are one in the same. Rough up the crank shaft surface so the new seal breaks in and forms a complete seat. The rest will take care of itself!
BigMike
