The most persistent and expensive engine oil leak?

[DJP15]

Gearbox

[vanzep]

the gearbox side crank seal (AKA rear seal) is a bigger job and best time to do it would be when fitting a new clutch (also a good time to look at lightened flywheel if this is somewhere on your list) but im not sure if ive ever had this is 20+ years of daily driving a lude - it can seem like a rear seal but can turn out to be oil dropping from above ie/ vtec solenoid or dizzy cap or cam cap. But i think the rear seal can weep a little without being a massive issue and most prelude gearbox housings will have some oil coating the inside. I guess it only become a big issue if there is a lot of oil loss and/or it is contaminating the clutch plate(s). I would make sure the diagnosis that it is clutch fluid is definately correct. You could take a sample and send it to a lab. Other thing to think about is that oil leak from cambelt side can run across the underside and look like a gearbox oil leak.
It is relatively easy to check the gear box oil level and to top it up or replace it. Last time i did this from an inspection pit it took me 20 mins to drain, fill and check the level. Hope this helps.

[CARRisma]

I know that this is a year on from the last entry to this thread, but I am new to the forums after seeking help with my own Gen5.
After one singular frosty morning in Dec 21, my Prelude developed a more aggressive leak. After taking it to several mechanics who wouldn't help (and charged for the privilege) I found a more honest guy who told me a bit straighter.
He said similar to this thread, that it could be driveshaft issues, and that seems to be the only issue I recognise here that could match my issue. I find a small puddle of oil often on the driver side area of the engine. The car still drives wonderfully, but I don't want to get caught out by leaving this too long. (And I don't want to oil stain everywhere I park lol.)

Only issue is that my guy said it would be super expensive to get to the issue. It's been classified as a gearbox leak (manual transmission) and he says it's a huge mission to get into and poke around to find the cause. I just want to ask if there's any quick tricks to identifying where it may be coming from that will confirm whether or not I have to take the gearbox out to fix? The main diary of this thread has shown that the individual jobs aren't that expensive, and long story short I don't have £1000s to drop into this. My whole budget would be around £1000 max, and that's before fixing its bodywork.

Any tips on identifying if this driverside leak might be easier to fix than a whole gearbox removal? I hear these crank seals seem to be the biggest offenders?

Many thanks in advance for any help!

(Only just made an account here so haven't got all my stats and pics set up, but it's a 99' 2.0 Manual Gen5, 167,000mi more or less)

I'd put money on this being rear main seal (crankshaft) rather than gearbox.

Any progress?

Update on mine. Leak reoccurred last year. I didn't want the hassle of going back and forth to the same Honda specialist as last time. I wanted a more definitive diagnosis / repair so took it to PAW. Diagnosis is a warn crankshaft, where it goes through the seal, so if I want this fixed, that'll mean a replacement crankshaft which is an engine out job.

Also, it would seem that the rear main seal is leaking too as there's tell-tale oil under the clutch housing area.

[DJP15]

Thanks for the reply!

That is what my mechanic has also come to the conclusion of. The seal.
At the moment I'm just running it and allowing the leak to happen sadly. It lost about 500ml over the course of a month or so. I'm just spending some time putting it back in the garage for a top up until I get a new vehicle. Any engine out job or huge money sink isn't particularly economical at this point for my car, as it's been rotting for a long time. (Previous owner kept it in a container and I think that's left it to rust faster over 6 years he had it in there.)

I'm going to have to put money into it before its next MOT in October 22, but until then I'm just going to keep it ticking over until the time comes to move it on.

Many thanks for the input everyone!