Front differential problems

[NevDavey]

Bought our P reg 4wd 2.5td Freda in Feb. On purchase it had same newish tyres all round but front ones were rapidly wrecked - all tread removed on inner edges. Assumed this was due to having to fight steering on m-way with camber. Bought new tyres of right size and had tracking adjusted. It did the same tyre wearing thing, was a bit hard to steer and still had to fight against camber. Was told camber thing was due to original tyres being for snow use (presumably they run at lower pressure than I was using?). Replaced worn front tyres again. Also had tracking laser checked on all 4 wheels. Persevered with new (road) tyres on front - better, but noticed they were wearing unevenly on the tread blocks with more wear at the front of each tread block than at its rear. Was very busy at time and had to run vehicle regardless. On trip down M5 to a job in Devon there was initially a loud whine from the front and a smell of gear oil. Slowed and stopped at next services - couldn't identify prob or see any leaks etc. Carried on until (in horrid rainstorm) noticed through nasty oily crud on rear windscreen that Freda was emitting cloud of smoke. Bigger smell of gear oil. (Apols to any oily following drivers on that day). AA'd home, job postponed. This was, of course, just beyond the 3 month warranty deal I received on purchase. Took Freda to local autobox man whose eventual opinion was that the front diff breather had been blocked, (possibly by underseal), oil had been pressure cooked (was black) until breather self-unblocked, oil erupted like volcano and diff internals wore rapidly with no oil in. Now running fairly smoothly with front prop shaft removed - slight singing whine from front diff on occasion but nothing compared to noise (above 30 mph) from front diff when prop shaft is reconnected. There's a bit of vibration around 65 mph which may be due to uneven tyre wear (or perhaps a bit of slacknes without propshaft?). However, I bought a 4wd and would still like it to be one, so...

Where can I get a decent used diff for not much cash?
Are all Bongo/Freda front diffs the same?
Are front and rear diff internals the same?
Could it have had the wrong size internals fitted prior to my purchase?
Is the pressure cooker explanation the only likely one?
What else should I consider checking out before I spend cash on this?
Might I get away with just replacing crown wheel and pinion or will the bearings and seals be suspect too?
Is running in 2wd putting a strain on the transfer box?
Can I think of any more questions? Probably!
Have you got any answers?

[dandywarhol]

I think you've hit the nail on the head about the breather - I've preached that one a few times - underseal is often the culprit Sounds to me like the viscous coupling at the rear of the autobox is also fubared