Some will take the shaft out after 75-100k miles and put lube on the splines of the shaft(2 piece shaft). If you do this, there are alignment markers(usually paint on Fords) that must be lined back up when putting it back together as it is balanced in that position. If you get the alignment off, it will ruin your mid bearing and your u joints. I had this problem with our county shop after taking out our F450 ambulance's shafts for various reasons.
2012 Sandpiper 365SAQ weighing @ 15k, Onan, 2nd air, slide toppers, TST
2013 F350 6.7L Lariat 4x4 CC DRW,Viair 1007, Ride-Rites, Edge CTS, B&W
2001 Chevy 3500CC DRW 4x4, 8.1L, 4.10 gears w/ Detroit TrueTrac
2001 Ford Excursion Limited 4x4 7.3L,V/B Spring Mod, ProComps, Hellwig Swaybar, & other 'Necessities'