gearshift problem 3rd to 2nd 2.0tdi 6spd

[cfcorp]

Hi,
My 2005 tdi passat six speed has developed an annoying fault when shifting from 3rd to 2nd when driven a while
It doesnt do it when cold, it shift up 1st to 2nd to 3rd no problem all the way and all the downshifts are perfect except 3rd to 2nd when driven a while. it will downshift from 3rd to 2ndwhen the speed is around 25 -30mph and sometimes higher, it doesnt grind, i downshift from 3rd to 2nd, push in the clutch like i normally do, push the gear lever into the 2nd gear position and me doing 30ish mph, it might move to like the neutral position without any noticable grinding or obvious popping, even if i hold the gear lever in second and lift up the clutch i dont hear any grinding or feel anything odd. i notcied it made a grinding noise only today but on one occasion for a second or two after a load of 3rd to 2nd shifts. I can get it to more or less downshift all the time if i am around 30mph or less with lowish rpms. it seems fine cold though i will definitly confirm that first.
Last year i changed a seal on the end of the main gear shaft as it was leaking slightly but the shifts were always good.
i topped it up with total BV 75-80 API -4+ after draining it. if i remember it took less than 2ltrs and drained out about 1.8 litres.