Should I "exercise" the locking rear diff?

The 2019 manual (pg 302) says, "at least 10 miles each month." That time interval and distance is not at all practical for a lot of owners, and Toyota surely knows that. The words in the manual are from their lawyers, for liability minimization reasons. The words in the manual have little to nothing to do with actual, known, tested failure rates. I am sure there are owners of Toyota 4WD vehicles (especially in climates with little to no snow) who go many years without ever engaging 4WD. If it was so mechanically vital to engage 4WD-H on a regular basis there would be pop-up messages in the dash for the owner, and also sensors to detect lubrication levels. As others have mentioned, there are differences in the mechanicals with older vehicles, and maybe the manual's guidance was more relevant in past years, but they leave it in the manual anyway.

 

This pink taco 4L is clear…

 

Just my thoughts, it seems like a good idea to use the 4 highs , 4 lows , crawl controls, and lockers and a few other features to insure all the systems are working , correctly too…. The “saying you don’t use it ..you lose it” has some truths too…
No harm to engage all those systems on a regular schedule..be it , every few weeks, months, semi- yearly…0r when you feel it should be tested or used..

If you never engage those systems…it can get frozen from non-use? Or …when you need it …at least you know how to work it..?
My camper windows locks ( rains a lot)…the locks do get hard to open and the seals around the windows will
get struck…I will lube them often…and open the pop-up side windows on the camper…(when you do not open often, the seals will stick…

Use it or lose it…. “Prevention is better then any cure”
Aloha,