Success. Thankfully it is an open hole, so have managed to drill out the old one. Bit of filing to get rid of some of the remnants and have ordered the relevant Helicoil set. Will also need to clean up the threads on the other stud holes as they are full of crud too.....


1972 4/4 4 seater, 1981 MGB GT
1984 Harley Davidson Electra Glide, 1990 Kawasaki ZX10