Hi Grafos, can you confirm if it's either engine oil on the exhaust or is it manual gearbox fluid? The manual gearbox fluid will have a specific smell to it distinct from engine oil. Just smell some off the oil dipstick, then open the gearbox filler plug and smell some gearbox oil, you will smell the difference. If it's engine oil, it'll most likely be the crankshaft rear main oil seal, it can also be the main seal for the gearbox, hopefully they renewed it when they had the box out. Don't laugh, i know many people me included once, who've ordered the clutch kit and "right, let's get to work!", only to realise we've completely forgotten the rear main oil seal as well as the seal for the gearbox! Just ensure they actually change the seal. I know a few fokes who've used some of those chemical products, Rislone produces some, that claim to seal oil seal leaks. Have used one of those myself on my previous 97 CE Mitsubishi Lancer with about 243,000+ kms, you can see why i didn't feel like removing the gearbox on it to repair.. And miraculuously, it worked, it stopped the rear main seal leak. You thus want to ensure that they actively renew the seal that's leaking. If it's the rear main seal, if it were me, since I'll be removing the gearbox, good practise to renew both the gearbox main seal as well as the engine rear main seal. I'd go further and also renew the IRD seal where the driveshafts go in to since you will be removing both driveshafts, as well as the seal in the gearbox where the left hand driveshaft goes in to. Even though these others don't leak, it is usually a good time to renew them all given how cheap many of the seals can be purchased.