Hi everyone,

I’m reaching out for some help or shared experiences from other 991.2 GT3 owners — especially those who’ve dealt with RMS (rear main seal) issues on hard-driven or modified cars.

Car details:

• 2018 991.2 GT3 (6 years ownership)
• Tuned ECU and gearbox
• Full straight pipe exhaust
• BMC air filter
• Car is driven hard occasionally (including high-RPM pulls and light track use)
• Service and RMS replacements have all been done at Porsche Centre Pretoria

🔧 The issue:

My RMS has been replaced three times by the dealership. Each time, it was said to be installed correctly, using the proper tools. A crank pressure test was also done — no issues found. Here’s the sequence of events:

1. First RMS replacement: Paid for this one. The seal started leaking again after some spirited driving.
2. Second & third replacements: Done under goodwill (no charge). Each time, Porsche test-drove the car gently for 100km, and no leak occurred.
3. However, as soon as I got the car back and pushed it a bit (not even at full track pace), the leak returned again.
4. Most recently, I did a few proper redline pulls (8,500–9,000 RPM) with some friends and the leak got worse — then stopped again a few hours later.

🧩 Things we’ve already checked:

• Crankcase pressure: Tested and confirmed fine
• Crankshaft runout: Not officially reported as out-of-spec, but no measurements were shared
• No CELs, car runs great otherwise
• Oil leak is always small but noticeable — not massive

🔄 My concerns/questions:

• Could crankshaft runout or endplay be subtly out and only show under high load?
• Could a faulty or weak gearbox input shaft bearing cause crank movement and RMS failure under stress?
• Is it possible for the RMS to temporarily seal again after driving?
• Are there heavy-duty aftermarket RMS options anyone has used successfully with track-driven or tuned GT3s?
• Has anyone else had similar issues after tuning?

Porsche is now telling me the next step is potentially replacing the gearbox, which feels like a huge jump considering there’s no evidence of internal failure.


Any advice, experiences, or direction would really help me out. I love this car and just want to enjoy it without stressing every time I drive it hard.
vv photos are attached below at the end of the message vv

Thanks in advance!


GT3.Chaos
This is as big as the leak gets. Make 5cm +- in diameters.

 

That’s a weird one. When the leak shows up, is it always in the same spot or does it move around a bit? Also, after those redline runs, does the car smoke at all or just the oil drip? Makes me wonder if the crank vent system might still be building a bit of pressure even though it tested fine. I’d love to know if they actually measured the crank runout or just said it’s “fine.”