I assume that, by oil cooler, you mean one for the transmission, right? In that case, a number of us have bought a B&M cooler, but I can't remmeber the part number. I think I bought model number 70255. I think.
As for switching to synthetic, do you mean engine oil or transmission fluid? I didn't switch my SVX to Mobil 1 synthetic until well after 100k miles. The only problem I have is that more oil leaks out of the seals now. I put about 3,000 miles on the car a year and I lose about a quart a year. That's really not too bad and well worth using the synthetic, in my opinion.