We had a Hoover (Logic summat or other) for ~15 yrs (3 or 4 repairs in that time), and currently an AEG that's we've had for about 6 or 7 yrs. Both were washer-driers and both seemed to work quite well as both washer, and drier (contrary to one or two opinions in t'other thread) - tho' we don't use the drier that often.
The only build-up has been mould in the second machine after we started using non-bio liquid in it - and even then only up in the powder tray area. Periodically I get a brush in there and give it a good scrub/rinse, and if you're using non-bios you need to run a periodic maintenance wash (empty, hottest setting, with some bio powder).
But even then, we've never had any slime build up elsewhere or on clothes.