head gasket, etc.

After reading the many posts on synthetic lubricants, I decided today to take my 73 450 sl in to replace engine, transmission and differential lubricants. I took it to a new mechanic, as he was open today, Saturday. Here's what happened.

For the engine, he used Mobil 1 5-30, which is what he says he uses in all his cars. I have been using dino 20-50. I seemed to recall Mobil 1 came in 15-50 or 15-40, and I asked him whether this would be better. He said no, the 5-30 was right, and that the viscosity numbers were not the same for dino and synthetic. This doesn't seem to make sense to me; isn't 5-30 viscosity the same no matter what type of oil? At any rate, I went with the 5-30. Does anyone have any advice on the right viscosity.

For the transmission, he said I needed Dextron III, and he didn't think there was a synthetic equivilent. He called someone and they confirmed this. He said to leave the transmission alone; I replaced the fluid just about 12,000 miles ago. Was he correct on this?

For the differential, he said also there was no synthetic equivilent for the recommended product. Was he correct on this?

Now, for the head gasket, etc. I have had very slight leaks since I bought the car about 1 year ago - the occasional drop of engine oil and the occasional drop of transmission fluid. I was recently told by another mechanic that the valve cover gaskets were leaking, and I replaced them. (Afterwards. I looked at my records from the previous owner, and found they'd been replaced about 15,000 miles ago.) At any rate, the mechanic today said it did look like oil had been leaking from the valve gaskets, but that this had now stopped. However, there was still some fresh oil leaking -- but very little - and this he traced to the right rear head gasket area, and accordingly said the gasket needed to be replaced. About 6 months ago the car started to run hot and needed a new radiator (I'm not sure how hot, or for how long it was running hot, as my wife was driving the car at the time). He thought I might have blown the gasket due to this. However, I don't think I have any other indications of a bad head gasket. There's no oil in the coolent, the car doesn't burn oil, the car now runs pretty cool all the time, compression seems fine. My question is, do I need a new head gasket? How long can I wait to fix it, and am I doing any harm by not changing it. I'd rather not have the leak, but for the $$ involved, I think I can live with it. Do both head gaskets ordinarily get changed at the same time? Also, what else should be done if anything as the same time as the gasket change? The car has 112,000 miles. The mechanic today did say that leaking motor oil would damage the suspension rubber.

Regarding the transmission fluid, two mechanics have said it's transmission seals, and two have said its the power steering pump, which does appear to have a slight "weep." I think I can live with whatever it is for now.

Thanks for any advice.

Further to my own post, a friend has suggested I get the heads retorqued, to try to stop the leak. Has anyone had any sucess with this?

Regarding the synthetic atf and differential fluid, I checked the Mobil 1 and Amsoil sites, and very clearly there is Dextron III equivilent synthetic atf, and also synthetic differential oil that I'm almost sure would work. Guess the mechanic didn't know what he was talking about.

[engatwork]

The 240D got Mobile 1 synthetic in the differential, regular Dextron III in the tranny and Delo 400 in the engine yesterday. First oil and atf fluid change since the rebuild on the engine. Don't know when the rear differential was last changed but where that Mobile dripped out of the different is a clean streak

[jsmith]

synthetic + older engine = leaks. if you were running 20-50 and switched to 5-30 synthetic i would expect the engine to be sopping wet with oil. synthetic oil seeps into nooks and crannies like nothing else...