Aqua clear 500 which is now AC 110. I have 2 on my 90 that have been running continusly for 15 years. Only replaced an impellar on one.
http://www.bcaquaria.com/forum/showthread.php?t=14886&highlight=20+years+eheimOne of my old Eheim filters 2217 was making a weird noise, so I took it apart and the ceramic shaft was broken.
I've had this filter for about 20 years and this is the first problem I have ever had with it.
I went by Big Al's today to see if I could find a replacement shaft for it and figured there was no way I would find one, but, they still make that model and had a replacement shaft in stock.
I checked out the price of a new 2217 filter and it is about half the price I paid for mine 20 years ago.