At £40 a hit (x3) plus the seal kit, I'd start getting a bit bothered then. But, sure, if they're knackered, my dislike of their cost won't change them.
As carbon said, if the oil is milky you have piston or seal problem.
If it is overfilled that suggests that quite a lot of water has made its way into the piston housing.
If the low pressure seals are gone you will usually see water dripping under the pump but not if the drain holes are gunged up.
Some washers are prone to making the oil milky due to a poor seal design. The old KEW 3 piston pump was like this. You could fit new seals and pistons and in a few weeks the oil was white again!
But Kränzle is a good quality pump and it shouldn't happen under normal use.
It's not hard to take off the cylinder head and have a look at the pistons and seals.
A common cause of damaged seals is running the pump dry or leaving it running on bypass too long, the water gets hot as it circulates inside the pump and quickly damages the seals.
