Car is a 245DL with about 194k miles, may have a small leak coming from the rear (rear main seal has been changed about a few thousand miles ago), oil doesn't drip down on the ground but does get spread on the tranny pan when driving. The source of the leak is unknown but oil does collect at the place near where the two tranny cooler lines are clamped, on that bracket/clamp piece, close to the plastic "grille mesh" on the bell housing.

I know this has been talked about so many times, and the most recent one was about synth mixes, which prompted this post. I've been thinking about switching to synthetic for my next oil change but hearing these stories about leaks caused by synth made me rethink and reconsider a full synth switch. So then I thought about using the synth/dino mix that is offered by most oil brands...until I read that these mixes could mean a teaspoon of sytnthetic to one qt of dino (I'm just exaggerating here, but you get the point) and so basically one really doesn't know how much synthetic oil is added when you are paying a premium price for such a mix. In the most recent post about synthetic oil, people have said you can make your own mix. Here are some questions:

1. I understand the viscosity grade of dino but don't know much about synthetic. What dino viscosity do I use with synthetic?

2. What is the best synth/dino mix? 2qts synth/2qts dino? 1qt synth/3qts dino? Etc.

3. Best brands to use? Mobil 1 and Mobil X (dino viscosity)?

4. I've read that once you switch to synthetic you can't switch back to regular dino oil. Is that true for synth/mix too?

Thanks!