1998 E39 525tds Manual Gearbox/clutch Trouble

[demc7]

Car = 1998 E39 525tds (Right Hand Drive) 5-Speed Manual, 75,000 miles

The car has been running perfect until recently. Most of the time it is ok, but sometimes when I select 2nd the gearstick locks and won't allow me to put it into 2nd. This happens whilst driving. If I try again, it finally gets in. It is very frustrating! The same problem happens when selecting 4th, but not as often. Is this simply the clutch needing replacing (hasn't been done in a while) or is there another problem in the gearbox?
If nobody has any ideas I'll try and provide more details.

Thanks

[bad man working]

Chech your the hydraulic sytem for leaks. Slave cylinders on the left side of the gearbox and the master cylinders by the peddle. If you need the proper way to bleed it email me through this site and I'll let you know