right now it has been running for almost 5 hours without more then a few seconds of delineation. So I guess it is not magnetized after all.
The hairspring appered to be the problem there. When I "banged" the watch is was a mere gentle rapping, not a hard knock. I would not expect a refund from a delaer anyway, so I do not intend to return the watch. If it happens again i will certainly bring it to a watchsmith to fix.
Thanks for all your help - so far its pretty accurate 8)