Would it be a good idea to take off the rakes and wheels and grease the bushings or just let them run dry? What is the life expectancy of these bushing.
Grease the rakes with the zerks. No lube is necessary for the other bushings. The axles use steel bearing housings with PTFE(Teflon)/Aramid(Kevlar) polymer bearings. The rake shaft in the blower housing also uses the steel bearing housings but with more conventional nylon 6/6 polymer bearings. Nylon 6/6 does work better when oiled (or wet for that matter), but as these are only piloting a shaft with little load so you shouldn't need to. I've never seen them wear out even on 500 hour units.
Both of these should last the life of the unit but are easily replaceable at low cost if need be. The shaft clearance is only a few thousandths. If they move more than that you could pop off the tapping screws from the steel housings and slide out the bearings to inspect them.
http://nyliner.com/type5_6product_info.htm
The above is the link for the type of polymer bearing used. These are superior to sintered bronze bearings as they need no maintenance.
PK