Here is what Lee has to say about the current part (3rd Generation):
There is also this support article: Identify version of Load Master primer trough assemblyLee Precision wrote: There was a third generation design change on the primer feeder effective October 27, 2011 eliminating nuisance damage to the primer sliders and trough cover during operation. Formerly the gray cover and trough, now sold as an assembly along with the primer slider, primer lever, 6-32 x 1/4 screw and o-ring. These parts are no longer available individually. This assembly replaces parts: LM3254, LM3253A , LM3253B and LM3251.
The reason I wanted to hit on this is that the article did not identify the original version of the assembly and there is no telling how many are still in use. I had one in my #1 press and it was causing all kinds of problems that the new generation cured immediately.