Before you replace the heater most common cause of heating failure is burn out of the thermal cut-out. (also called thermal fuse, overtemp cutout and probably half a dozen other names) These are a small screw on device on the exhaust duct, when exhaust air reaches too high a temperature, like a blockage, they fail before a fire.
examin the exhaust duct inside the dryer for devices that look like this or like this with wires connected to the terminals. there may be 2(hi lo), test with a ohmmeter -conductivity good, no conductivity replace.
there are only a few different kinds the local parts guy will have them all. take the dud one for him to match.