Front wheel drive axles consist of constant velocity ("CV") joints, which are filled with grease and contained in rubber enclosures called boots. You can check the CV joints and their boots when test-driving a vehicle with front wheel drive: first turn the wheel all the way to the right and slowly accelerate, then repeat but this time steer all the way to the left. A bad clicking noise from the axle indicates an axle problem. Visually check the axle boots, and see if is grease thrown around the inside of the front tire area or on the tire itself, either of which indicate a broken boot, if not an axle that needs to be replaced. This can be an expensive project, between the parts and the labour.
Front-drive transaxles generally share their oil supply with the differential, though some older Chrysler front-drive automatics have separate drain and fill plugs for the differential (but use the same transmission fluid),
However, if you have a 4 wheel drive vehicle, the transfer case and rear-axle differential housing have their own oil check and fill plugs. These gearboxes typically use SAE 80-90 gear oil type GL-5, though in some cases they need special factory oil. Check your Owner's Manual, if unsure.
In normal city driving, you should change the oil every two years, though if giving your vehicle hard use, you change the oil annually. If there is no drain plug, you need to siphon the oil from the differential housing. You should also check the level at the fill plug during every engine oil change.