Let me guess that your water pump failure was the slot in the drive shaft where it engages the adaptor "tang" wearing down. If so, that's a common alignment issue. A new shaft is available at a fraction of the cost of a new pump and the rebuild is easy. I had two or three of these "go" until I got the alignment perfect, now have about 1000 hours on it with just the slightest wear. There is a special alignment tool that Perkins had, but I have not been able to find it, so I've had to do it just 'by eye".
Out of curiosity, what period of time is your oil consumption of 0.5L? That's about what I burn in an all-day (8 hour-ish) run, which is more than I'd like, but tolerable.
Craig Briggs - s/v Sangaris / SN68 Tropic Isle Harbor, FL