The great advantage of the Alessi 9090 to me is the ease with which it can be filled with hot water. I'm very pleased with mine. Although I have bought some spares from
Redber I have yet to use any of them, despite having once let my 9090 boil dry. (Looking around for suppliers I see that the UK distributor is out of washers for the 9090/6 and 9090/M at the moment.)
Leaking (or a bit of hissing) has never been a problem just a sign that I've overdone something when playing with grind size and/or fill.