As above, I've a tiny tiny pinhole in a cast ally sump, What is the best putty type stuff to use?

I take it the best method is to drain the oil out, degrease and key the area?

You know there was an advert for JML sealant putty, looks like that could well do the job once degreased..

No need to drain the oil, just bung some soap (from a bar) in the hole, key the surface with an abrasive pad then cover with jbweld/chemical metal etc.
It's what we did as a temporary measure a year ago as we were a couple of hundred miles from home, and it's still oil-tight now

[Edited on 18/7/10 by UncleFista]

You could try planishing the hole first, get it really clean then tap away with a ball pein hammer.

couldnt you tap it out and put a small screw with a washer on to seal it. or just use a self tapper.
adam

Another vote for JB Weld

Halfords do a pritt stick type thing that works well

If you're going to the effort of draining, I would get it brazed...

Surely someone near you must have an AC TIG welder! If you were near me I'd do it for you happily. Epoxy will never be a permanent solution, merely a band aid cure!