I have a U1252B, but am interested to see how the OLED replacement/upgrade goes on the 3. It'd be great if a newer model display with better performance can work.
The 1252B isn't easily upgradable as there's a 3rd board for the OLED models. Board #2 is different as well between the two different display types regarding the display driver chip IIRC.
That said, you're better off with the U1252B's LCD display anyway (mine's 8 or nine years old, no broken display yet). Backlight is very nice, and it has improved battery life (~9hrs vs. ~36hrs for the LCD version per the specs).
The OLED might give you ~5 yrs of service if you're lucky.
And regarding battery life, I keep 8.4V, 300mAh rechargeable NiMH batteries ready to go. Not only are they convenient, but they're less expensive in the long run as well. One last tidbit, the battery life spec on the U1252 is based on a 7.2V unit, so an 8.4V unit will extend your battery life as well.