Use a TORX key (no. 20) (from Screwfix B&Q etc) to undo the screw and the plastic panel just pops off, I've just fixed mine now, same symptoms as you had (on my Concorde 320)
Underneath the panel I found the belt attaching the drive shaft to the shaft of the mower cylinder was loose. This was caused by a loose cap(crankshaft pulley) on the top of the drive shaft which should be firmly attached by a cotter pin. The cotter pin had snapped, I managed to get it out and replaced it with a small nail (bent around), which seems to have done the trick. I also had to drill out some melted plastic from the inside of the cap to get it to fit back firmly on the top of the drive shaft.
Plastic had got inside the cap when it had come loose and moved outwards on the shaft where it started rubbing against the plastic cover and melted some of the plastic.
Martin, July 2014
