[TR] TR4 rear pinion seal replacement

[Randall]

> There's supposed to be a cap?  

None of mine have had a cap.  

But it sounds like a good idea, I may see if I can add one when I build a
3.45 axle for my TR3.  In fact, given how dusty it is around here, a proper
breather filter seems like a better idea.  I see MMC has a variety of them,
starting at just a buck.
http://www.mcmaster.com/#vent-breathers/=6xijw7

Randall