If the fittings are screw in type, go ahead and change them. When they are out, clean out what you can. If they are press in, I would leave them alone and add a little heat to the area. It doesn't take much to sofen up the old grease. A hand heald propane should do it. You might try taking the hose off your grease gun and cleaning it out with solvent. Then refill the hose with solvent of your choice and use the grease gun to force it through the zerk. Joe