If you can gain access to the core plug, then remove it by either punching it through with a screwdriver and then levering it out, or drill, screw a self tapper part-way in and then pop it out with a claw hammer. Clean around the lip of the casting where the new plug will seat, apply a small amount of sealant such as threadlock, then knock the new core plug in nice and square with a suitable sized socket.
Les.
Thanks, job done, but needed the nearside exhaust manifold removed, and one of the engine mounts, replaced two core plugs, one was corroded with a pin hole leak, the other because I was there already, seems it was just a dodgy spec core plug made from crappy material, since the second one I removed had no signs of corrosion.
Managed a trip to Aberystwyth over the mountains, lots of snow drifts on the A44 :D
I really need to consider some new rubber for the Winter months, and front & rear diff locks, since I did cross axle once on the trip.
