Richard,
Thank you very much! I have been suspicious of that because the white area is not particularly white. It just plain looks dirty.
I took a Q-tip wet with water, and stuck it in alcohol. The cleaning result is not immediately apparent, but I'll check it tonight.
I appreciate that MMC will help refresh the tritium. They are right there when needed.
Meanwhile, I may not return the slide. It has been hard-chrome plated by Tripp Research in Texas and I'm reluctant to go through all that again if it got lost during transportation.
Thanks again for the tip.