Since I bought the SL, I've used the M-P almost exclusively with the (1972 vintage) Summilux 35mm v2 and the (new) Summarit-M 74mm f/2.4. Seems the pairing of lenses made for me on this camera, given that I have all the other focal lengths in R lenses on the SL where I like to use them more for various reasons (but mostly because of the better close focusing range and nicer viewfinder, to my eye).
I purchased a new Elmar-M 24mm ASPH last year. It's a wonderful lens, but I'd hardly used it. Probably should have gone for the 21mm. This thought was gnawing at me a bit over the past few months.
And everyone who's used the Tri-Elmar-M 16-18-21mm f/4 ASPH, endearingly called the WATE, has been singing its praises. Hmm. Three ultra focal lengths in one ultra lens. Works great with the M-P due to the EVF. Said to work great with the SL as well. Hmm. $5000. Hmm.
Found a mint second-hand WATE for sale at one of my reputable dealer friends' shops. The gentleman selling does trades. How much with a trade? Well, a lot still, but a good bit less than the above when considered together.
My bank account is lighter, two lenses are traveling now, one will arrive there, one will arrive here, and next week I'll see whether everyone singing WATE's praise is just pulling my leg.
I love/hate this stuff.