Thanks, Craig. I will be sure to pass that on to my dad.
Yeah, it's a funny thing about my dad's dementia that facts often come to light in unexpected ways, which upend our assumptions. I had always understood that my dad bought this grill new in the late 60s or early 70s, but a couple of years ago he said, "Oh, no, that's not it-- I bought it at a garage sale after your sister was born". Which was really fun for me to think about him scoring what was already an old grill at that point in time (almost 10 years old then), and also a partial explanation for my interest in used grills. ;-)
The bigger mystery at this point just came up a couple of days ago. My mom gave me her diary from 1970, mostly musings about me as a baby (apparently I ate solid foods very early on, which also explains a lot). But what intrigued me were several references to my dad cooking ham, potatoes, etc., "On the Weber". I asked him what grill he owned before the Imperial, and he doesn't think he had a Weber before 1974. So either he's forgotten about an even older grill, or my mom is using the term 'Weber' for another grill (like ubiquitous brand-names such as 'Kleenex' or 'Xerox' or 'Band Aid').
Bottom line, though: I just cooked on an almost 50-year-old grill, and I'm pretty happy about it.