On the front seal problem of a G28 /13 gearbox - I did a few other checks and noticed that when I put a skinny screwdriver near the front seal and pry a bit - you hear compressed air escape for a few seconds....
So I looked around and there is no breather that I could notice - however there is a red plastic cap at the top cover which is an airtight plug of some kind only. Then I did a brief search and this came up :
"...If you are constantly changing gearbox oil seals, check the gearbox breather for plugging. When breathers become clogged, internal gearbox pressure can build and find its way out through oil seals creating a false impression that the seal has failed. This can become more problematic during summer months."
There clearly is no breather on my gearbox - and the thought now is whether to add one or not......exchange the red plastic thimble with a brass oval piece that permits tiny pulses of air through it.
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'80 928