what mechanical seal did you use?
Peter from PeMoPa did not use mechanical sealings but simple Simmerrings.
As far as i know he now is trying to use also Burgmann sealings.
I have some of the newer, lower Burgmann sealings here
Maybe there is also on of the old version left. I'm not shure.
I suppose the belt could not be tenioned so high that it will bend the shaft of the pump.
Although i always did use little bit more tension than the spring could offer.
If you left only a little amount of water you may do nothing and watch the things for a while.
Maybe there is something little between the sealings surfaces or the surfaces have to run in for a while.
What about the surface of the shaft?
I had a garden pump leaking where the rubber part on the shaft has a puncture hole.
Maybe your shaft is somehow raw and ist therefore leaking some water between the shaft and the rubber part of the sealing.
No bearing failure, everything looked fine. No play, rotated beautifully
Seals bought from Westcoast seals in England, the ones I mentioned earlier.
The shaft looks in good condition
I'll try to upload photo's.
The ceramic seal has two sides, (obviously), one side is flat, I put this towards the rotating seal, the other side is slightly grooved. This is the way the original seal was fitted, Did I have it in the wrong way?.
Unless anyone has any other ideas, then that's the only solution I can come up with.
I think I might replace the bearings again, and clean and fit the original seal, after a close inspection under a magnifying glass, but it looks fine.
OK about to look up how to post photos.