Can't say I've fiddled with an Ariston machine, but I have recently been doing a bearing change on an Indesit washing machine, which involves removing everything! Door seals are fairly straightforward but fiddly. There is a springy retaining ring which holds the seal on the tub. If my Indesit is anything to go by, there will also be a retaining wire to keep the seal on the front panel. This wire seal has a spring fitted to it to allow it to stretch for removal/refitting. A bit of care with a slender implement is required to winkle this out. Once you've got both retaining rings off, the seal just peels away. To make putting the new one on a little easier, I used a (very) thin smear of a popular washing up liquid to help the rubber lip fit on the rim of the tub and the front panel, but this might not be necessary. You'll want your slender hands and fingers to get in to put the tub spring ring on. Make sure the children are out; they shouldn't hear what you say when you're doing this bit.
John Webley-Jones, August 2012