So back in 2015 I built a printer that is a cross between a Repap Wilson I and a Wilson II, with a Z Probe, dual Z-axis stepper motors and LCD running on Marlin. In late 2017, I accidentally pushed new marlin firmware (v1.1.9) and, since none of the proper changes were made, proceeded to not work (shocker right?). The old version of Marlin refused to compile, stating a missing file related to U8glib. I spent a solid 2+ weeks trying to figure out how to fix it.
This past week, I was looking at the MMU2 and thought "oh hey, i could mod my old printer and .... oh right" and so I took another look. This time, I was actually able to get it to work !!! That being said, I'm now running into issues I cant figure out, and I'd rather not take another 1.5 years to figure it out.