The auto tranny heat exchanger, being made of aluminum, is apparently
susceptible to internal corrosion. Under ideal conditions, the cooling
system is a happy, minimally-corrosive environment; but of course
conditions in some people's vehicles are often...less than ideal. When
the exchanger gets eaten through, generally that means the tranny is
toast. It's also not good for the cooling system, as I understand it,
requiring a lot of flushing, and wailing, and gnashing of teeth...
But apparently you only really have to worry about it if you don't
know the maintenance history of the vehicle. GoWesty recommends
replacing the heat exchanger every ten years as a preventative
measure. Some people totally bypass the issue by tossing the exchanger
entirely and putting in a separate transmission cooler.

On 5/14/05, Robbie Cotner <robw_z@yahoo.com> wrote:
> I'm looking at buying an '89 Vanagon GL with a bad auto tranny.  According to the owner the transmission cooler blew a seal and coolant was pumped into the transmission.  The tranny now does nothing when put into any gear.  I assume this means the trans needs a total rebuild?  How could this be prevented from happening again?