I have an 04 heritage with a 4.2 that has 175,000 miles on it. I have an oil leak that I believe is from my rear main seal. If my PCV valve wasn't working/ or is just worn out, would changing it stop that leak or is the rear seal done for? I wanna get the motor back to good condition so I can do some mods. But if I should cut my loses and shot for a motor swap?

 

The rear main seal isn't difficult to replace, just time-consuming. Manual or automatic trans?

 

Usually on any high mileage engine when the rear seal starts to leak it's because of excessive wear at the rear bearing. The crankshaft now with a little wobble in it beats the seal out until it starts leaking. I could tell you to just replace the lower end bearings and seals but I can assure you the rings are already starving for oil from the bearing wear and the rings will start pumping oil if full lubrication returns via the new lower end. So either live with the oil leak, rebuild what you have, or get another engine or truck. Considering you've gotten 175,000 miles out of it, you got yer moneys worth. I'd suggest a junk yard engine and build what ya want.

 

It's an automatic. I've considered on starting a build on either a late model roller 5.0 or maybe a 3v 4.6, but either way it is gonna be costly. The truck is my first truck and I've had for 6 years. Any ideas?

 

If you do an engine swap, you will also have to swap the tranny unless you do use an old 5.0 (302) due to bell housing bolt patterns. The 4.2 uses the Windsor bolt pattern. The only modulars that use the Windsor bolt pattern are the very first 4.6's from cars.

 

Well I think I'm just gonna replace the seal and hope it lasts long enough as a crutch until I can get a built 2v 4.6 put together. I don't want to put my daily driver under the knife without being certain of the outcome. Thanks for the advise guys and if y'all have any tips or suggestions on this, please let me know!

 

The tranny has to come out to change the rear main seal. I'd let it leak till you are ready to put the truck under the knife. It's not going to hurt anything, it's just gonna be a bit messy. If you had a manual trans that would be a different story, a leaky rear main can gum up the clutch.