Series 2a gearbox problems

Hi all, can anyone HELP!!!!!! I have a 1959 series 2a landrover SWB. The gearbox is very grindy ie: it sounds like a shaft somewhere in the housing is catching. Whats the best thing to do, change the box or change the shafts and bearings. Also can you fit a s3 gearbox of a 6 cylinder onto a s2a if the bell housing is changed. And 1 last question as i'm still learning about landrovers. behind the housing for the gearbox is a small pipe which is dripping oil, i've hear dit is a pressure relaese for the engine but not sure, can anyone help.
WHEN I'M STOPPED THERES NO GRINDING, WHEN I ENGAGE GEAR AND SET OFF THE GRINDING STARTS.

hi, [gearbox] well iam just fiting s 3 box and 200 tdi in a s1. box in ,engine in today looking good so far . Do you want to keep it the same stock ? I WOULD GO FOR S3 BOX ,.little BIT more work ie clutch mas/cyl and slave/cyl think ive sort how to do this shell be doing it this week .you keep the same clutch pedal .. will do some photos when ive sorted it,, if this is any help ..

you can change the box to a s3 but on a 6 cylinder bell house one stud hole is different, plus on a series 3 the the slave unit is on the passanger side. mt personal feeling is a s2 box is a better gearbox than a s3. but its up to you

The series 3 box will go in on the same mountings, if your gonna take the bellhousing off the s2 box your halfway there to stripping the gearbox so you might as well see what's wrong with that one and repair it,they are a lot stronger than the s3

I'm with Mathewpink, IMHO the series 2 box is stronger and less prone to throwing sinchro detents than the series 3 box.
As to your mystery pipe, not sure. Try following it to its source.
good luck

series 2 and 2a boxes are weaker on the lay shaft especially the earlier ones than series 3s ,much better box