I found this random leak of something very very thick and greasy with no particular smell there's a little smell maybe like oil but u can barely smell it.

Can it be engine mount leak since octavia has hydraulic engine mounts or some previous oil??? or something serious.

Oil 0.2 - 0.3 per 15k km which is normal

So idk im out of ideas

I'd suggest you give the area a good clean and then keep an eye on it.

Edited 30 July, 202530 Jul by ords

I could barely clean it with break cleaner...imma keep track of everything for the next week to see wtf js going on

If it is coming out of an engine mounting, it should be showing up where it is escaping from, the hydraulic fluid that escaped from my 2011 Audi S4 engine mounting was black, and unfortunately there was only Audi genuine parts available that were "like for like" for that car and so other ones, a bit hard on my wallet, but maybe forgotten about now, almost!

You can always hope that there are some good quality aftermarket hydraulic engine mountings available for your car.

In the end I just wiped off what I could, it was mainly showing up on the S4's aluminium subframe, and the under covers hide that, what I initially spotted was a wet/moist looking "thing" - that was the first time that I had eye balled these engine mountings, I found that during an annual service/inspection, so caught it early before that engine mounting failed completely.