Components
Driveshaft (with U-joints or CV joints), front/rear differential, transfer case (4WD/AWD), axle shafts (with CV joints on most modern), wheel bearings/hubs.
Drivetrain is the unsung system between transmission and wheel. Service it on schedule and it lasts the life of the vehicle.
Differential and transfer-case fluid is the most-skipped service. Cost of skip: $1,500–$4,000 in replacement.
Driveshaft (with U-joints or CV joints), front/rear differential, transfer case (4WD/AWD), axle shafts (with CV joints on most modern), wheel bearings/hubs.
Differential fluid 30–60K (sooner for towing/severe), transfer-case fluid same. U-joints: grease at every chassis lube if grease-able. CV boots: inspect at every service — torn boot kills the joint fast.
Yes — plus the transfer case or center differential. Many people skip the front and pay for it later.