not sure on these but they may be similar to Peugeots,have someone operate gears and check the gear linkages for wear,there may be a couple of rods to check,also there may be a linkage under the gear lever which caused problems on Peugeots and seized up,if all is well with gear change system then you may be looking at getting the g/box out for a look at the clutch for wear,also the g/box may have internal problems,good luck
cdc
June 2013