Regarding standard transmission oil changes.

One of the reasons I've been told why transmission oil changes are not
required like engine oil changes is that the tranmission oil is not
subjected to combustion by-products.

We change the oil in the engine because the oil loses many of its
"good" properties as the engine is running. There is no debate over
this issue.

Since the transmission oil is isolated from the ignition combustion
cycle, the oil lasts much longer.

However, if one is inclined to change the oil on a frequent basis, say
bi-annually, it certainly won't hurt the transmission.

Drew Jenkins  86 Synchro
drew@sunrise.com