I use the LEE auto drum powder measurer on a Hornady LnL press. I sold my Hornady powder measurer, right after I got it in the package, used it (almost exactly like the RCBS measurer), and went "back" to my auto drum. Had one, sold it with a RCBS turret press that I was using it on, and then purchased another to use on the LnL.
I know I have powder on my shellplate when loading, for me that is just a cost of "doing business" as I always have one or another case shake just a bit of powder out of itself due to the motion of the shellplate. .....or possibly the auto drum "is" leaking, I don't know. My LnL is used primarily for pistol loading, and I haven't had any problems due to powder charge yet. The loads are always within spec when I check them; maximum .2 grains of a charge specified for the case....usually they are 0-0.1 grains and leaning closer to 0.
For whoever cares, all 3 of the brands (RCBS, Hornady, LEE) of powder measures that I have used in a "progressive" situation have had leaks from the case of one sort or another while charging on either the turret setup or 5 station progressive. All were used with their respective automatic case charging system, and all had powder come from between the case mouth and their drop /measure activation system. It is normally only a very few grains of powder, and that is after hundreds of cases. A bit of pressurized air, or a small painting brush, and I am ready to go again.