Hi Ali,
The reason for the use of oil is that some greases will be too think and inhibit the bearings ability to function correctly, with a light oil such as Tri-Flow it keeps the bearing lubricated and allows the roller and needle mechanisms withing the bearing to function as they should.
With regards to the bronze bushings, it is best to follow the recommendation in the manual and use a red or high strength loctite to secure the bushings. I always do this and it is best to clean the surfaces of the bushings and also the recess in the housing to make for a good bonding surface.
Hope this helps, and any questions give me a shout.
Cheers,
Ross