A Defender of the age of my vehicle has a sophisticated “air conditioning” unit, otherwise known as an open vent to allow inward air rush (shown in the first image). Like a lot of other fittings the pins which secure it were corroded and prevented one of the vents from opening properly. We thought it would be a good idea to replace this with new ones (lubricated with copper grease). The dome nuts on the old pins were resistant to unscrewing with all tools tried (it’s kind of hard to get a proper hold on them with a socket, for example). In the end we cut through the pins with my Dremel 300, using the 38mm metal cutting disc. There is a little amount of damage to the hinge metal closest to where we cut, which we might be able to cover with paint. In all honestly, those just join the long list of chips, dents, scratches and blemishes on the body work of a vehicle of this age. Anyway, the vents open much better now.