Thanks for your reply's, I will replace the waterpump as soon as possible.
I already planned to do so, but wanted your confirmation. I know how to wrench, but lack your experience and I don's want to replace something that is ok.
Last summer I did some work on the engine, valve guides, timing chain and rails and piston rings. I put a lot of work and sweat (even in the Netherlands it can be hot) in this car and now it runs great. I want to keep it this way.