Mustang Man, If you are having problems which you attribute to lack of glow plug help in starting the engine..but find no obvious faults... consider using the glow plug hole reamer... carbon slowly builds up around them and insulates their effect ...so you get the symptom without them being bad in any other way... I think they may have one in the rental program...check the sticky's at top of page...
The FSM says to apply heavy grease to the threads when you do that.. to capture chunks .... and then to use compressed air to blow out the rest...
Don't use the engine turning over as that may suck it into the bore depending on the start position of the piston ....