Maintenance Question

I have a 91 toyota camry with 214k on it. The previous owner took extremely good care of it and the engine is in excellent condition. He used castrol gtx 10w-40 in it and changed it religiously every 1500 miles. The engine does not leak or use oil. This summer, I will be commuting to work in the car which will be about a hard hour's drive each way. I want to keep the car for a few years, and am wondering the best way to continue servicing it. I really like the mobil 1 synthetic oils and would like to use one of those, but am not sure which grade. I am aware that putting synthetic oil in it could cause it to leak, but i would be willing to sacrafice some leaking for more wear protection. They don't make a 10w-40 synthetic, so I was thinking of using 15w-50 which is the next step up but am concerned that might be a little too thick. Should i do that or should I continue using dino juice and change it every 1k?

Also, the previous owner couldn't find the owners manual so I have no idea what kind of lubricant to use in the transmission (manual). If anyone could help me on this i would really appreciate it.

A 10W30 should be fine, depending on your climate. 10W30 should be fine between around -18*C and +38*C. Don't worry about leakage, I gaurantee you will not have a problem. I hear this so much it's strange, but I have never encountered this, nor have I met someone who has had this problem...it always seems to be a friend of a friend who had that problem. Read the last FAQ on this page: http://www.mobil1.com/USA-English/MotorOil/Synthetics/Myths.aspx

I don't know off hand what weight oil to use in the transmission, so just ask the people at the place you buy the oil from. Better yet, phone the service department of a Toyota dealership.

Of all the cars I switched to synthetic, only one had a leaking problem, but it was an older engine with all cork gaskets. They dry and crack, then the solubility of synthetic oil cleans the junk out of the cracks and it leaks more. For the most part, import cars use rubber and paper gaskets which don't suffer from this (rare) problem. If they do, run some stop leak in it :)

Edit... by the way, slutty patton is correct, 10w30 was probably specified in the manual and will do fine, but one call to the dealer will clear that up.