In defense of the plain ground glass screen that came with this MX -- I have for many years preferred plain ground glass screens. I got into the habit of using them back in the mid-80s because of a few optics I owned that were rather slow, rendering a split screen with micro prisms virtually useless, and an annoyance since it was in the middle of the screen, thus blocking my view. It did take some getting used to, using a plain screen, but I managed, and finally got to where I preferred it, regardless of the aperture and focal length of the lens I was using. To find correct focus, I rock the focusing ring back and forth, such that I'm going in and out of focus in both directions. I decrease the amount of travel as I rock the ring until I've found best focus with little if any focus rocking at all. It's not so difficult when using my method.
I can second Jon Goodman as being
the source for light seals. The instructions he includes with the kit are themselves worth the price of the kit. My experiences with Jon are, when I contact him about a seal kit I need, his response typically is that he'll send them out right away and he's trusting his customers to be prompt paying him for the kits. Not too many businesses like that left in this world. The above link shows an email address for Jon that I don't believe is valid anymore. The one that he most likely will respond to is:
JGood21967@aol.com