I love my Parker 51s. All of them older than I am (of course) but the ones that still work (aren't cracked, etc) work wonderfully (filled with Noodler's inks).
Of course! I've got a couple actually, they're useful in my other hobbies.
The capillary filler is still a beast to clean, though. It's not so much a matter of it getting crusty with dried ink as it is that it's designed to hold the ink inside.
I've built two things to address this: the first is a rubber bulb with a length of clear medical tubing that just fits over the back of the reservoir. This lets me force water and cleaning solution through the reservoir with a modest amount of pressure, flushing it out. The second is a felt-lined holder with a spot for a rag or paper towel in the end. I can chuck that in my lathe, put the pen in it with the nib facing away from the chuck, and turn it on low for a few minutes. Centripetal force forces the ink (or water) out of the reservoir, through the feed, and into the paper towel - aided by capillary action, of course.
They’re a pain to clean thoroughly, though, so they’re best used as a pen for someone who doesn’t change inks very often. That person is not me :)