Hi, I recently noticed a slow coolant leak from my 2012 Mk6 golf GTI & after being serviced by a local mechanic he mentioned that it was from the thermostat housing area. I've done quite a bit of car maintenance in the past & decided I'd replace the thermostat housing myself & while I was at it do the water pump just in case. Disassembly has gone fine, but I'm not feeling great about how the new (non OEM) pump has gone in. I'm hoping that I might be able to get some advice from the knowledgeable folks here on the forum. The water pump is from Machter Auto parts where it is listed as compatible (picture below).

Water Pump Assembly Fit Audi A4 A3 TT VW Tiguan Jetta Golf GTI Eos Beetle 06H121026 - Machter Autoparts Online

Its an aluminium housing rather than the original plastic one, but there seems to be plenty of articles online that this, in itself isn't a problem & some suggest may even be better. There are 2 other design differences to the pump that came out. The temp sensor is fitted slightly differently. Mine had a kind of clamping plate, while the new one has a clip that fastens it in. Its a little bit wobbly with the clip, but seems ok. The main difference is that the interface where the top radiator hose attaches has a slightly different design. The mating fitting on the hose end then doesn't seem to seat tightly against the tapered section of the pump. There is perhaps 1 or 2mm of play. ie you can push the hose fitting 1mm past the point at which the clamp clip slides into the groove in the pump. I took the 2 o-rings shown in the picture below off the pump as these weren't on the one I removed. I am assuming they might be for some other VAG model car that also uses this pump (but I could be wrong).

I have a few questions:
1. Does anyone have any experience with this particular pump? Is it intended to use the o-rings? When I tried them they don't seat particularly well, seeming to slide up the taper.
2. Can anyone give any guidance about the apparent looseness of the top radiator hose fitting? Is my pump perhaps not compatible with my model of car or is it just a less than ideal brand?
3. I'm leaning towards getting another brand pump. Can anyone recommend a supplier? I'm in Sydney if that helps.
4. An unrelated question, but I found the spring below under the car while I was working on it & I'm not yet sure where its from. Its 13mm dia x 25mm long. Any suggestions?

Thanks so much in advance for any help.
Brett