It's a bit hard to advise you at a distance.

A helicoil is a wire thread "insert" which is threaded into the hole. Obviously, an oversized thread has to be cut first to receive the helicoil which is then wound in with a tool.

The critical operation is the cutting of the thread to receive the helicoil - it must be dead square to the sealing washer surface or the plug will leak.

I would recommend that someone conversant with the procedure does the job - it takes practice to get it right.

Another approach is to thread the hole oversize and use a larger sized plug. This still requires accuracy to work. As with any repair job, the skill of the operator is paramount.

I would regard a new sump as an unnecessary measure - with care and skill, either method suggested above will work. Aside from the expense, you may have consequential problems if the sump is changed. If a repair job fails, the sump can be changed as a last resort.

659.

skerra 52 - good luck with the repair. About 12 years ago I wrecked the thread on the engine block of a Merc 190E when I cross-threaded a new spark plug. Luckily, a skilled neighbour performed what 659 describes and I had no problems for the rest of the time I owned the car. It took him a few hours, though.

Probably too late for you now but the sump is about £80 to buy and less that 1.5 hours to change. helicoils always eventually fail there a great repair for a thread that isnt likely to be reused once tightened but on a sump thats a different matter, your sump is alloy and not especially thick where the sump drain bolt is located

regards peter