On previous cars of mine, the breather hole was to be found facing rearward, at the location described in Morganatica.
IIRC, it was suggested that this (small) hole should be checked and/or cleared, by gently inserting and twisting by hand an appropriately sized drill bit.
May I respectfully suggest that your specialist looks again, it is a very small hole!
On the Salisbury axle there are also small outlets/holes near/on the backplates diagonally opposite the grease-nipples, alledgedly to vent grease if over-lubricated.These might also help vent the axle ?
Andrew Green
Glorious Devon
2002 Plus 8 Le Mans 62
