The main shaft seal has failed on my auto transmission and I now am only getting about 200 miles per quart of fluid. What is the best way to change this out? Is it best to pull the engine and separate the engine from A.T. and can I pull the seal without opening up the A.T.? Thanks for any help.

Your post is very confusing. I assume you are adding transmission oil every 200 miles, not engine oil? How do you know it's the main shaft seal, not the rear main seal?

Either one, I suggest you find a shop to do it. It's normally a job too big for a home mechanic.

From Proman: "...not engine oil? How do you know it's the main shaft seal, not the rear main seal?"

I pulled the engine last year and changed out the front and rear crankshaft seals, camshaft seal, installed new timing belt, etc. The rear main seal had broken in three places and the oil consumption had dropped to 600 miles per quart and made the car look like the Exxon Valdez whenever it rained. After all the work oil consumption dropped to 4,000 miles per quart (250,000 miles on the engine). Anyway, I should have looked closer at the trany seal back then, but I didn't and now can't remember if it is changeable once the torque converter is separated from the transmission housing. If the housing has to be opened up then I probably won't tear into it again...do you know if it can be changed without going internal to the housing?

I believe so. I replace the rear main on my 88 Camry last year. I pulled out the torque converter and checked the seal on the tranny side. It's still soft and firm, so I didn't replace it.

You should check the service manual to make sure.