I've had a 2026 and 2028 for about 7 years. they both have leaking problems, especially at servicing, but then it goes away after a couple of days.
1) the large o-ring between the motor housing and the basket holding tank needs replacing every 2-3 years. that solved most of the problem.
2) get a small container of plumber's silicone grease. liberally coat all o-rings after servicing - the main gasket, where the double-taps fit into the motor housing, and aroung the priming mechanism. silicone is kinder to rubber than vaseline. this is per tech support at eheim.
3) often water will leak out from where the wire exits the motor housing. this is the tough one. i think the o-ring inside the priming mechanism needs to be replaced (i've never done it, but i think i'll have to. you should be able to find a kit online.
4) i've had a plastic tray under each canister to catch the leaks. at first i had a disposable ladagna tin, but my brackish water corroded a hole right through it!
5) i first noticed the problem when the power went out. test the filter by unplugging while it's still full and attached, and check for leaks.
It's a great filter, but the leaks are really frustrating. i expect better from eheim. hope this helps.