ok heres the thing about rear main seals.
if you have a manual transmission you should fix the rear main seal ASAP because it leaks on the clutch disc and will cause the clutch disc to saturate and fall apart.
on a automatic its a lot easier to let it slide beacuse youll just be leaking oil and as long as you keep the engine full you can leak for years without anything else but your driveway being effected.
NOW if your going to replace the rear main seal you need to first see if its a 1 piece or 2 piece seal!!!!! this will decide the cost of your replacing it
2 piece rear main seals are the cheapest to replace the are typically easy and require only dropping the oil pan and using RTV silicon with new gaskets.
1 piece rear mains require you to pull the crankshaft assembly to properly replace them. at this point I will always do a full rebuild kit.
piston rings and oil control rings on the pistons.
main bearing and rod end bearings.
i will aslo use a micrometer to check the crank wear to see if its in tolerance.
at this point the engine has to be out of the vehicle so i do head gaskets and anything else that may be a foreseeable issue like valve cover gaskets and intake manifold gaskets water pump timing chain or belt.
For me when a major repair demands taking the engine out it saves me money to just fix it all that way its all done and new and i know it.
a friend of mine replaced his rear main seal and 4 weeks later he spun a rod bearing and broke the block it couldnt be saved he had to buy a new engine 3200$
if he would have taken my advice the 400$ master rebuild kit would have replaced that spun bearing and saved him a bunch of cash.
low range offroad offers full master rebuild kits to fit any level of skill from full piston replacement to simple re-ring kits.
4Runner Engine Rebuild
