Aye, sump doesn't look too healthy but I've just seen earthman says he's got a new one to fit - which is why he wants to undo this joint of course! Have you done one before earthman? If not then be prepared for a bit of a fight if the one still on the vehicle is original factory fitment as the gasket cement is pretty tenacious! When fitting the new one don't be tempted to use too much sealant - of course you do need to use "enough" - the problem with using too much is the surplus will get squeezed out from between the joining faces and some may break away, fall into the sump and get sucked into the oil pickup filter mesh. this will reduce, or possibly block, the oil supply to the rest of the engine with predictably expensive ramifications!
My boy's Punto -2012 1.4 8 valve - had this type of joint in this position on it's exhaust. The Pandas have a "sleeved, push fit" type joint here with a side clamp round it. - well ours does anyway?
I was a great believer in Copper grease and still use it for "general" purposes (Copa Slip being my favourite - I like Aluslip too for use where aluminium components are used) However, following all the "hoo Ha" about copper grease corrupting ABS signals - a problem I never experienced despite using it for years on many many different makes of vehicle - I decided I should join the recommendation to replace it with a ceramic based grease for brake work. Looked on line and bought this:
View attachment 446057
It seemed to work but it's quite thin and a bit "runny" and I noticed there didn't seem to be much evidence of it when doing the next service maybe a year later. So, having been used to the copa slip being still much in evidence even a couple of years later I asked one of my favourite wee local garages what they use and they, after confirming that copper greases should not now be used on brakes, recommended this stuff:
View attachment 446058
Which just happens to be what my local SRS Motor Factors have on the shelf. Maybe that's why he uses it? Anyway, it's much more the consistency of the copper grease and I'm much happier with it, it's pretty much replaced copper grease when I'm doing brakes. I use silicon grease on slider pins because they often have rubber parts which many other greases will attack and degrade.
Now to get to the main point of these ramblings. Ceramic grease works splendidly as an antiseize on stuff like exhaust fittings, such as we're discussing here. I am using up the silver hook in this way. You'll find the heat burns off the "greasy" part of the grease and leaves the ceramic part behind to protect the threads. The ceramic residue seems not to be "slippy" - as grease is "slippy" - and therefore seems not to cause these fixings to slacken in use but leaves a white protective residue behind which greatly cuts down on the rate of rusting.
Having said all that, I've now had the time to research brake greases in more depth and once I've used up the Granville product I'll be buying a tin Permatex, this stuff:
https://www.midland-mustangs.co.uk/shop/permatex-24125. It's suitable for use on the back of pads and other palces, as an antisqueel, but also, because it's a synthetic formulation and not derived from a petroleum source, it is suitable for use on slider pins etc too. (doesn't attack rubber) It is a wee bit expensive but one tin will last me just about for ever just doing the family cars.
My boy's Punto front flange bolts looked exactly like those in the OP's picture - you really wouldn't think that it had been a nut on a threaded fixing! - I noticed that the gasket was keeping the two halves of the flanges slightly apart so I used a hacksaw with an 18tpi blue blade to saw down into the gap and through the bolt. This, of course, damaged the gasket, but I was fitting a new one anyway. Then all that had to be done was drill out the wee bit of stud left. I've had varying success trying to drill out bolts like this - I think they work harden with the heat and vibration - and, over the years, I've broken quite a number of drills in the attempts. Cobalt drills, although expensive, seem to work quite well on this sort of job. When assembling with the new exhaust pipe just use a nut and bolt with an all steel locking nut if available but I've used a spring washer and standard nut many times, as recommended by Mike above, a nylock nut is of no advantage as the system gets hot enough to melt and burn the nylon which turns the nut into simply a standard nut.