Guys
Purchased a secondhand 120 that the guy had been using a mineral based oil in, I have since run it using Redline and am getting an excessively large amount of very black oil residue over the cowl and fuselage U/C etc. I have only put three tank fulls through it so my question is do you think that it will eventually come good or does it need some sort of intervention?

Keep flying it and eventually the Redline will clean it out. If you are using the same mufflers the original owner had that is where most of the goo is.

Redline will clean her out for sure as BigBird mentioned.
you could also be running a bit rich as well.
Not a bad thing for now..helps clean out the gunk I would surmise.

My DA-120 is running 40:1 Redline. It is also spitting the black gunk all under the fuse, L.E. of stabs etcetera...
I'm NO engine expert, but am leaning towards thinking perhaps it is a bit rich. I plan to very gradually lean the high end and see if it clears.

Thanks for the replies, I will just keep running it and clean up the gunk after the flight