Hello,
thanks, JFP in PA and 911monty!
Edit: checked parts numbers. Only piston changed. But it makes sense also to change the spring.
Well, if you don't have access to special tools or you're not able to fabricate the needed tools yourself and have somebody to do the job, than i think you run into cost problems, because even independent Porsche workshops ask in general for a lot of money, just because it's a Porsche. And so it is quite expensive to maintain these cars if you need a workshop to do it.
I do all maintenance stuff myself and do also more advanced jobs on the car. To me it is fun to do things like that, because i can see results immediately - which i don't do in my job often. But it takes time and a lot of research to do it right. And sometimes i have to do things twice. Like my axle boots, where i put too much grease in it and at a longer ride on the German Autobahn at vmax one axle boot just "exploded".

But this time i know how to repair it and it will take less time than last time. Also now i have an Oetiker plier.
Regards, Markus