First project achieved!
Thanks everybody for your help.
There were enough pointers along the way for me to get lucky and finish the project.
I went back to the geek shop and ended up buying a 30
hm: resistor rated at 3W.
I calculated the stock fan's output:
12v/.44mA = 27hm: (about 5W)
Then to approx. halve my speed, I calculated what another 30
hm: s would give me:
12v/60 = .2mA
&
12v x .2mA = 2.4W
So I went ballpark and bought a 30
hm: 3W cement resistor for 64yen.
It was only a bit more for a pack of 2 pots, but the resistor looked nice and easy to solder and other people had reduced their same model computer's fans to 50% speed with a big noise reduction and minimal thermal gain.
This machine had been used to salvage parts for others, so after the fan mod, I did a bit of drilling and cut a piece of the PCB off to accommodate a cool little red push button for power (about 200yen I think at the same electronics parts store).
Still a total electronics newbie, but it feels really cool to have fixed a machine I would have just sold as junk a year ago
Thanks for all the advice, I'm sure my solution is nowhere near perfect but I will be studying up more and with the help of electro-tech-online.com will be challenging myself more soon.
Cheers,
Leon