I know the machine Darren, its a good un

WD40 is sprayed INTO the blower via the small metal flap that's on the front panel of the machine. A good 10 second squirt at the end of very day.
Just for your info,
Change oil every 50 hrs
Oil and filter every 100 hrs
Grease the two nipples on top of the blower every 100hrs
Clean our the filter behind the jet in the header tank every 100 hrs or more often if you live in a hard water area.
Change fuel filter every 200 or 300 hrs
Change spark plugs and engine air filter every 500 hrs
Change blower oil and water pump oil every 500 hrs
If the machine cuts out at any time it will usually be caused by water in the header tank overheating, this happens when water is flowing slowly through the machine. For example when cleaning upholstery or moving lots of furniture and not moving wand.
To prevent this from happening turn the thermostat down in these situations.
If it happens on a job you can bypass the overheating protection by removing the last of the fuses in the machine ( back fuse). Start machine and turn thermostat right down, this will cause hot water to empty from the header tank and cold water to re fill.
Re fit the fuse, turn the thermostat to a lower temperature and continue cleaning. DON'T run the machine for too long with the fuse removed, you will have no protection against machine overheating.
Hope this helps
Cheers
Chris