[Billwill]

Bear in mind that glow #3 and Glow plug #2 sometimes could have the harness swapped over....so maybe it is not actually #3 failing!

Before removing #3 try swapping the connectors over on the two glow plugs....if fault still calls out #3 then there is nothing wrong with the plug itself but is a wiring problem ie. bad connection or wire chafing to engine.

before pulling out the injectors try using a good brand Diesel Injector Cleaner in the fuel tank.