5-20 oil

Yes - called static and dynamic seals.

If it's the right consistency, it would - like a gummy sludge that
builds up being closer to a solid as you move through the seal/shaft
interface from inside the engine to outside - takes years to form.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Your hunch is wrong. And it's not just rope seals. Ever seen cracked
neoprene gaskets? Not being a mechanic, you likely have not - but
trustme, they harden up and crack with age. As long as there is a good
film of varnish/crud covering the cracks and the joints between the
gasket and the engine parts, little if any oil gets out. Wash away
that film, and you have oil sneeking out everywhere.
Same thing happens with paper type and cork gaskets as they dry out.
Same thing happens with neoprene lip type seals, and specific to the
Mitsubishi engines, the rubber cam plugs.
A dirty high miler 3.0 Mitsu is virtually guaranteed to leak oil from
the rocker gaskets, cam plugs, and camchaft seals if switched to
synthetic or flushed without replacing those seals and gaskets.
Good chance of rear main and front main seals as well, but not nearly
as common as the top end.

 

I've been a hobbyist for 38 years, and a mechanic for 25 of those
years. I've owned and worked on cars aged from 1928 on up. I've
rebuilt engines, resealed engines, and repaired engines on vehicles
from Moscavitch to Rolls, in the northern and southern hemispheres,
and on both sides of the atlantic. Doesn't matter what kind of car, or
where it is driven, if not properly services, they ALL varnish and
sludge.

Gaskets are seals too. And no, I have not bothered to remove that kind
of crud from shaft seals - but I've replaced seals that had ample
evidence and accumulation of crud on them that were in bad enough
shape they would have been leaking a WHOLE LOT if they had been clean.
Not only that, but enough varnish build-up on the shafts themselves to
form a "second lip" that the seal ran against .

And 5W20 is not the only synthetic oil in use today.

 

I'll grant you that sludge can make

And if you go back to my original statement I did not specify only
rotating components.
I stated that switching to synthetic oil on a high mileage older
vehicle could very well cause the engine to start leaking in many
places where it had not leaked significantly before - particularly on
a 3.0 Mitsubishi engine in a Chrysler.

I stand by that statement.
The statement about sludge plugging galleries etc was in response to
the engineer questioning the mechanical properties of sludge and
varnish in regards to plugging leaks.

 

Of course I have... but I've never seen a cracked neoprene gasket or
seal that was NOT LEAKING already. Simple crankcase pressure variations
(going from slight vacuum under high PCV action to positive pressure
under hard acceleration (no PCV + blow-by) is easily enough to overpower
any hypthetical "film" covering a hypthetical crack in a gasket.

Not being a civil person, you likely haven't actually read anything I've
written particularly thoroughly, either.