Also just oiled the fan on my Halstead Best 60 as it had become horribly noisy, now it's like new (I wouldn't use WD40, use light mineral/instrument oil without PTFE). Not difficult to do and the service manuals are available online. I also had an ignition problem where the boiler would not light from cold, i.e. in the morning, but would when warm. Turned out to be the HT cable to the ignition probes. The insulation on one of them had developed a crack and was arcing to the metal case, resiting / redressing the cable cured the fault and it has been working perfectly for the last two years.
BTW, the fan is not for cooling the boiler, but drives the flu gasses out, boiler does not switch off due to overheating but due to the combustion chamber pressure sensor detecting the fan is not running.
Strictly speaking all these things should be fixed by a Corgi registered engineer, which I am not!