Warrantech and most other aftermarket warranties fail to become cost effective if implemented after the factory warranty has expired. After 100K miles Warrantech usually wont do much of a warranty. With over a quarter million miles I think you are just a tad beyond the cutoff. Even if they would write a policy they would inspect the &)(*%$#) out of it. I doubt you'd be able to pass off a problematic tranny and get it covered. Besides, the cost of the policy on a car with that many miles would cost more than a tranny rebuild.