We have recently bought a Mercedes Vito 52reg 110 CDi van. The gear change is stiff and it has now started crunching when trying to select 1st or 3rd. The other gears at the moment are fine - just stiff. If you change into 1st and hold the gearstick firmly in place you feel it click into place but 3rd crunches all the time. It usually tries and kick the gear stick back out when selecting 1st or 3rd. We are wondering whether the gearbox oil is low or needs changing?? However we have no idea how to do this or what gearbox oil to use or if this is even the solution. Help please . . . .