Re: 166 oil/variator
Lets get a few things sorted first.
1) The variator is unlikely to have any effect at all on oil consumption. The variators role in life is to alter the timing of the inlet cam shaft so that you can have low down torque at low revs and good gas flow at high revs= more power. All it does is rotate the inlet cam slightly when it gets the right signals from the Electronic Control Unit. If the car 'diesels' at low revs then the variator is knackered. If not, then the chances are that its fine.
Variators have been very poorly made, but Alfa did some ass kicking and I am led to beleive that the quality of these items has improved, but I don't know from when.
2) Any good quality 10w/40 oil is absolutely fine, preferably semi synthetic. Selenia is a brand name and has been made by a number of other producers, so it could say selenia on the outside and be BP on the inside. Its the QUALITY that matters, and most leading brands are good quality. Frankly its not something I ever worry about.
3) Blackness on exhaust tip?...Well, high oil consumption is usually accompanied with blue smoke on startup or acceleration. I doubt very much if the exhaust tip is being affected. The chances are the blackness is just residual hydrocarbons and nothing to worry about..just clean it off.
If on the other hand your FUEL consumption is high then it could be that your fuel/air mixture is running rich..and that would give you black at the back.
I'd step back a bit and just ask myself...Is the car running nicely, is the power delivery good through the rev range, is the consumption (oil and petrol) reasonable..Remembering that TS engines DO use oil and you need to check the level once a week, and NEVER let it get low.
If you add all these things in the likelihood is that there is not much wrong with the car, but I'l leave that for you to judge.
Good luck & hope this helps