Condensation in the engine?

[Dave C]

Another possibility to consider would be a faulty thermostat.

The only time I've seen condensation like you describe was in my non-turbo
'89 100.  The froth on dipstick was always there in the cold weather.
Eventually it became obvious the thermostat was not working properly ...
the heater couldn't warm the interior anymore (unhappy wife).  After
replacing the thermostat (87 deg C) we got a toasty heater (and a happy
wife) and no sign of froth on dipstick afterward.
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Dave C.