I agree with Randy, but have not had the number of water pump failures he's had. Anecdotally here, the Hepu used to be considered slightly better than the GMB, but not as good as the Genuine Volvo.

Anything that FCPEuro sells should be considered reasonably reliable. For decades now they've sold thousands of aftermarket water pumps for our RWDs and with their excellent customer service and lifetime guarantee would have stopped selling anything with a high failure rate many years ago. Another thing to consider with FCP is that they sell water pump and timing kits, which contain the Continental belt, INA tensioner pulley, Corteco seals and Hepu pump, all well respected by us shadetree types, so take that as a hint of their preference. They currently list the Genuine Volvo pump, and for less than half that price also sell Graf, Hepu, Meyle and Febi(Bistein), the latter two currently out of stock. Graf pumps are a highly rated brand in the aftermarket, also priced a little higher. Rockauto has the GMB at an extremely attractive price.

I think a lot boils down to quality control during manufacturing. In that regard the GMB used to have a poorer reputation (such as the stamped impeller occasionally coming off the shaft), but in recent decades seems to have improved, while reportedly the Hepu quality control (such as with their castings) has gone downhill a bit. Over the years I've happily used both Hepu and GMB depending on availability and price, mostly Hepu when I can find them at a good price. I currently have a GMB on the shelf waiting for the next install as I picked it up cheap from Rockauto combining it in my order to make for cheap shipping.

I'll note that in my then brand new 740 the original Volvo water pump showed a drop of green fluid down in the weep hole within the first year. Dealer service spotted it and said if I was loosing coolant they'd gladly replaced it under warranty. I kept waiting for it to get worse or for something else to justify leaving it in the shop for a day, but it never did, actually got better with age and within another year there was no more sign of fluid in the weep hole and I sold the car some years later still with the original pump. Go figure.

I'm currently chasing an increasing loss of coolant in one of our 940s that's been slowly getting worse for over a year. I know all the usual suspects, but have yet to pinpoint it with evidence. The top mushroom rubber do-nut on the water pump did need raplacing, and that seemed to slow it down, but it's still slowly dropping. That engine already had one head gasket leak a few years back, so hopefully not again, also hopefully not the heater core. I'm going to swap in another known good rad cap just for the heck of it then next maybe the water pump which has long passed its best before date and I've got one on the shelf, so like a 30 minute job. After that it will be time to get more serious about it possibly being the head gasket.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now