[PrettyBeast]

1hotm5, Thanks. The dealership confirmed there is only one part number for the original O-Ring: 17222245358. I had looked it up myself to be sure, and both the UK and US reference the same part number:
RealOEM.com   BMW E60 M5 Engine oil cooler/oil cooler line
BMW genuine parts order online www.online-parts.co.uk/bmw

The black one in the photo is the original. You're correct, it is thin and silver colour; it only appears black in the photo because it was oil stained. The surprise was that the O-Ring my indi removed is thicker than the original. It could be that the Oil cooler is after market. No more leaks for now even after hard driving; I've kept the original O-Rings; if it leaks again I will just replace the Oil Cooler------I hope it does not leak during my yearly autobahn/Europe run this summer

 

[PrettyBeast]

Hi JC, No leaks since I fitted the thicker rings, I've now driven almost a thousand miles.

 

[PrettyBeast]

JC, 1hotm5 makes a good point but the photo of your leak is the same as mine and I didn't have to replace the cooler. I was ready to order a new cooler but took the advice to first replace the rings, then the inlet or outlet pipes. It was a good advice and a good elimination process: 1. If it had been a crack, the thicker seals would not have solved the problem. 2. If it had been a damaged pipe the thicker rings would not have solved the problem. 3. If the rings and pipes had not solved the problem I could have used the them with the new cooler if I had bought one. 5. If I had bought a new cooler, I might still have needed to buy pipes if the old ones had been damaged.
The great thing about this forum is that the experienced guys can give advice that allows one to do some inexpensive elimination process before throwing cash at a dealership. I say you have nothing to lose by trying the thicker rings first; only a couple of dollars each. I say this especially because the photo of your leak looks like mine. If that fixes the problem, it means there is no crack and no need to buy a new cooler. It worked for me; I went back to get some spare rings. I went on a long trip and pushed the car hard, M all the way and no leak. Regular driving since then and still no leak. BMW could not explain why the original ring did not fit, they only said that different parts could fit different models: whatever that means! They also said that once the thicker seals are in place, and it doesn't leak immediately, it won't leak forever or until after the usual 50/60/100k mile wear and tear. The rings are easy to fit, you will lose some oil during fitting but I was advised not to top up until the car asked me to. It was a good advice, I always have spare oil, I topped up when the beast asked me to do so. Hope it works out for you: whether rings or a new cooler is what solves the problem, at least not so bad, we're not talking about major engine issues here

 

[PrettyBeast]

Don’t spend that money if you don’t need to, man. If after fitting the thicker rings you still get a leak, already knowing it’s not the pipes, then weld or buy the cooler. I say this because the cost of fitting the rings is almost nothing. I used my local tech but I was there helping out.

1. My bumper didn’t need to be removed, only the grill was taken off.
2. With the grill off, we gained access to the cooler and unbolted the screw. Oil was gushing out but this normal.
3. We had the rings ready, fitted it, bolted back the screw. As the seal on the other side was worn, we changed that too. It all took 15 minutes, he didn’t even charge me for it.
4. Not necessary but as a precaution, we removed the undertray at step 1 and jet washed the cooler after fitting the rings. We did this so I can see oil drops at my parking spot----no oil leak. I refitted the undertray after a week.

Perhaps I should have made a video clip of it, but I was told it was easy and it was. If you or your local tech can’t get access to the rings, the bumper is easy to remove. Sure you can get to the rings by removing the grill, though. Let me know if you need more information. Good luck, curious to know how it goes for you.

 

[PrettyBeast]

The grill has clips behind it. If the grill has not been removed for a while, the clips may be a bit tight to unclip so be careful not to break them. The grill just clicks back in place with a push when you're done. If you can, get another pair of hands to help but not absolutely necessary. I say this so you don't lose too much oil in between removing the bolt and fitting the new rings.

 

[PrettyBeast]

Hey Guys, Curious to know if the seals worked out for you?

 

[PrettyBeast]

I guess it was worth a try, good to know it's sorted out. FCS5, did the rings work for you?

 

[PrettyBeast]

Hey FCS5, I was looking out for your post, good to know you found the root cause. Ya cooler gets good looks, it is red colour? I want one It seems I was lucky that mine was not cracked, though new original O Rings did not stop the leak.

Hey M5 Jed, The thicker O Rings I used are still holding up nicely---after over 3,000 miles including hard driving. You can try them, only a couple of bucks each. I can't find a theory or explanation about why the thicker O Rings worked for me but the original thinner rings did not. BMW only said, "The thicker rings can be used for other models including E60 M5".