Gearbox problem

My gearbox (series 3 petrol) suddenly decided not to go into 3rd or 4th today, 1st 2nd and reverse are fine still. I have stripped the top cover of the box and checked the detent springs and balls, they seem ok. I have read that the problem may be the synchro springs broken or jammed on the 3rd/4th Synchroniser. Has anyone else experienced this problem? If you think it may be the synchro clips do you have any tips for changing them and do you know where I can purchase some?

There's a post IIRC describing this problem. detent screw on side of lever base? Shortsearch didn't turn it up but as I'm spending moretime repairing keyboard ("D" doesn't or repeats and spacebar just oesn't unless I use Landdrover special tool no.1 (ball-pein) I'm strugglingto search without google sarcastically asking me "didd you REEEEEEly mean....." and I'm eveloping a bit of an inferiority complex Search the threads and I'm sure you'll fin the answer. Themoral of this story is that wine is better in you than in your keyboardd....

Sorry just found post - (ddropthekidds) - diff problem. But I think same prob wasmentioned here sometime earlier - little searchingof threas should help...