I’d accept your offer though please read the below.
I don’t think it is particularly noisy for a 6 year old 40mm fan (I’m surrounded by them at work, most much noisier), it spins, but it isn’t quiet, and it is definitely a fair bit louder than when it was new. That is why I posted the video.
Prior to listing it (while it still had a couple of §drives in) I left it running Windows 7 for a couple of weeks, which it did fine, without any unexpected errors or failures to boot etc.
Having spent a couple of minutes googling; the only thing non-standard about the chassis fan is that HP have swapped the pin order vs the “standard” for 12V PC PWM controlled fans, and used a standard molex KK type 4 pin header housing instead of the special one you’re supposed to use for 4pin PWM fans. If you want to swap the chassis fan it is only a few minutes work to extract the pins from the connector, swap them over and cut off the ramp which gets in the way:
N54L Microserver – Rear Fan Replacement Guide
The PSU one would be a little more tricky to swap, but only involve a couple of minutes soldering if you’re happy working on that kind of thing. The PSU isn’t actually that non-standard (I’m surrounded by similar units at work – we use a different model from the same manufacturer in one of our products) – it is just a 1U flex-ATX PSU. (more info here: http://chrisstark.co/2013/08/hp-microserver-n36-replacement-power-supply-psu/ ).
What I would say to you is that if doing the kind of things listed above aren’t the kinds of thing you like to get involved in, then I’d actually prefer not to sell it to you. While the fans and the unit are working fine, there is of course every chance they >may< fail in the not distant future (things that spin eventually stop, that's why I've removed the drives), and of course if the above kind of remedial works are out of your comfort zone then the unit is a paperweight, so wouldn't represent good value. That is just a fact of life of buying an old second hand computer.
But if you are comfortable with the risk, and can repair this sort of thing economically yourself if it does fail, then at £50 delivered it is a steal considering the RAM, bluray drive, graphics card and WLAN card (which together are worth more than the unit).