2003 aircooled gearbox issues

Hi my 2003 1.6 air cooled t2 has a droning noise that comes from the gearbox…..the sound oscillates it is quite audible and gets louder as the speed increases. The shift is a bit stiff as well. There is also some slight bearing whine. Quite a bit of metal filings where on the magnetic drain plug when the oil was changed. Has anyone else had the same problem? If it needs a rebuild who is the best person to take it to? I live in Bristol Rgds David