They have had a number of problems with it latly, including door release faults. The guard I spoke to a couple of weeks back didn''t seem to think it would return very soon.
The problems that I have seen I think relate to the fact is that the "newer" drivers have not ever driven anything like that before and as has been said previous, don't know how to handle the gearbox correctly. I was always under the impression that you had to put the thing into 1st gear before releasing the brakes (as per the older t/c instruction manuals), certainly provides a smoother take off but alot of them seem to release the brake and then put it into gear. You get one hell of a jolt as everything catches up and engages which can't do it much good.
Of course one always forgets that driving 14x/15x units all day they probably don't get used to it that well but driving the old units does require a skill which is regrettably dying out. Having being given a chance to drive a 108 on several occasions (these being lightweight are "fun", especially when its wet!!!) I am all to familiar with the gear box techniques as they are similar to the National buses too - same problem, drivers "slamming" the stick through = rough ride = higher maintenance costs when gerbox fails.