8-year old Bosch washer stops mid-cycle

My Bosch WFF2000GB is about 8 years old and has recently (and regularly) started to stop part way through its wash cycles with water still in it, often during the rinse part of the cycle. It will normally (but not always) empty if ‘pump out’ cycle is selected so we can take the clothes out. Occasionally when taking the unfinished wash out of the machine – normally to get the help of friendly neighbours to finish it off – the clothes are quite hot even if on a 40 degree wash. Sometimes, the machine works OK for the first wash of the day, but it always then fails on subsequent washes.

I have ensured the pump is clear etc, but I haven’t yet checked the pump itself and I can’t tell if it is a timer fault. Do you have any ideas as to what the problem might be?

Over the last few months before this all started we were getting an unpleasant smell coming from the machine, which I thought was coming from the drains. Anyway, we eventually got rid of it (pretty much but not completely) by emptying out a clear reservoir connected to the outlet pipe; it was full of a grey slimy deposit. There is still some in the drum which I cannot clear out and which sometimes ‘spots’ clothes through the drum holes. Is this a normal residue from washing and could it be connected to the current problem? Is there anything else we should be doing as routine maintenance for a washer of this age?