You may find the oil leak is from the main crank seal and running down - it seems to run down and make the sump gasket look like it's leaking. To be fair the silicone rubber type gaskets don't really leak, that's why they are used.
Here's my 1999 HDi sump, I've just left it be the gasket looks wet but it's not leaking from there
mbell666 on here tried doing his sump twice and it still leaked, not sure of the final outcome actually on his. The Turbo can leak oil too which adds to the fun!
Cars in my care:
2021 Kia Spottage 1.6 Pez Turbo Dual Clutch Gearbox Trickery
2013 Renner Twingo - donkey work
I did mine twice after garage did my flywheel and clutch. I think they gave the sump a good wack when they put the gearbox back on.
First oil leak i had was the sump gasket but after that it was the crankshaft oil seal (that the garage changed at the same time). But i wasn't sure i got it right first time so did it again. Then the garage did it for a third time as they didn't want to do the crankshaft seal.
I would have a good clean round first, the sump gasket is not too hard but is a bit of a pain and best avoided if you can.
The 90 is probably easier to do as you don't have turbo pipe running under the engine to the intercooler, if you haven't got a/c then you should be laughing and its just drop it off clean it up and stick it back on. If you have a/c you have to remove the fan belt, the a/c pump from the sump (and tie it up somewhere) before you can take the sump off. MAke sure you have a good clean round the end of the block and sump, i'd apply the gasket to the engine block rather than the sump, seemed to work better.
Thats good info, will do this job next oil change and check the crank oil seal as you suggest.
Funny you mentioned the clutch as there was no obvious leak befre the clutch was changed but now there is. Not the gearbox or rear crank oil seal all around the sump bottom edge!!
I am voting for the sump gasket as the mechanic confirmed there was no leaks on the rear crankshaft oil seal when the clutch was fitted. A point I stressed with him when it was all in bits. It is certainly a good time to get that one sorted.