I know a auto trans rebuilder who does his re-assembly in a clean room.

The issue is partly that some of the orifices in the valve body are that small that a bit of grit could easily plug them. There are non return valves that use small balls, a bit of crud on the seat could prevent them from working properly.

Some may say that JKay is going over board. At least he can be confident that his fluid change will not result in a failure in the trans.

Unlike the motor, the trans wont run on peanut shells and coal dust !!

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving