How do I repair / replace the fan on my Baxi solo 2 PF?

My Baxi solo 2 PF failed to ignite recently, When I examined it the fan would not turn easily. I hit it with WD 40 and it worked again for about two weeks. It failed again for the same reason and again another dose of WD 40 for another two weeks. A plumber has quoted me € 500.00 (Rip off) The fan is basically working probably just needs to be taken apart and cleaned. Any help would be much appreciated.

Barry