Wheel bushings

Hello all.

Tractor is a Hechinger brand, 11HP Briggs, MTD model 142-669.

My front wheel bushings are worn out. I ordered a set of new ones from MTD parts using the part number in my manual. They arrived, and they are hard plastic. Question - should I put a lubricant on the axle when I install the new bushings, and if so, what should I use? I have some spray lithium grease from a brake project on my car. Would that work? Also, in the future, should I replace the bushings with bronze units?

The other question I have is sometimes when the tractor gets on really uneven terrain it stops moving, and I have to put it in neutral, get off, and push it out on to flat ground. Anyone have a clue what is going on here?

And is there a way I can tell when this thing was made from the model number? I know it is from sometime in the '80s.

Thanks in advace. This is a great forum!
John