Thanks for the responses.
I have the model HBW15 2.8RV which does not have a
dipstick. The oil level is correct when oil overflows from
the number 7 hole (as per Hurth manual). As I thought I
was overfilling I replaced the plug, in the number 7 hole,
with the nipple, clear tube and valve but on occasions I
I will check the breather hole but failing that I am
thinking that I will have to remove the gearbox.
My cruising areas of Caribbean Basin and South America are
at times so remote that a gearbox failure would be a
problem. Trying to find ATF in the Bahama Out Islands this
winter was difficult and checking gearbox oil level every
day and topping up with the attendant loss of oil from
overflow is messy and frustrating.
Thanks again - good have other opinions and experiences.