Mine does the same mate though if i shift slowly into second it doesnt grind. You said it though, 2nd gear synchro and depending on how long its been going on for the teeth on the engagement hub could be damaged. Oil change will be good for it but wont take away the grinding, best off getting the box rebuilt or get a replacement, 2nd gearset is the dearest to buy im near sure its about 290 odd quid.