I rebuilt sometimes ago my fan clutch as per tech tip on this site with silicone oil. The O ring was good and I put gasket sealer before reassembling both halves.

I noticed today that I have oily spots on the underhood as before the repair. The fan blades also have black oily deposits and the clutch too.

It seems that I have no choice but to buy a new fan clutch.

Any comments or suggestions

I'd try finding a new O-ring and doing it again before I spent all that money on another fan clutch. I've never had good luck re-using O-rings, no matter how good they looked.

It's also very easy to have the O-ring get pinched just a tiny little bit no matter how careful you are when re-assembling it. Or perhaps you could try a different ype of sealer this time and the problem will go away. If you used blue silicone, perhaps try the high temp red sealer this time.

Since you have done it once, you know how it's done.... and there really is nothing too difficult in doing the job, just the lost time re-doing it.