Honestly yeah I’d probably just grab the Lemokey; it has more capacity for repair and maintenance if the same thing ever happens to it. Most keyboards come with a key-puller tool and sometimes a dust cover now, but you can get one cheap if not.
While you’re waiting on it you could try putting some lubricant on the parts of the old keys that slot-into the keyboard - though I wouldn’t use WD-40. Maybe some bicycle chain drip lube like White Lightning (because it’s easy to find at a department store and it works in a pinch) in lieu of the PTFE Krytox oil we’d usually use for keebs. Just some dripped on a q-tip and swabbed onto the surfaces that rub-against eachother.
I actually googled it last night. I think the X3 is a typical “high profile” case where it comes up a little and conceals the lower sides of the switches. The X2 looks to be MADE as a low profile CASE (not to be confused with low profile keycaps or switches), possibly with a little clip or magnetic shroud to replicate the high profile look. It could affect feel and sound, I saw one review suggesting the X3 was disconcertingly “floaty” and an old-design steel plate low profile case would be more rigid, past the point where some people would prefer it. In this price range I don’t know that I’d get overly worried about it as long as it looks nice to you. You’ll be learning if this whole mechanical keyboard thing is even a big deal to you at all, and it’s really hard to say at first exactly what you’ll prefer.