Glow plug failures on 1.6L and 2.2L Kubota diesels

[Wildranger]

My Kubota has been grumbling on those cold starts, taking forever to crank, puffing out smoke, and feeling sluggish when it finally fires up.
Is this a classic glow plug issue, or is something sneakier happening?
What symptoms did you notice, and what fix finally got your diesel running smoothly again?

 

[deep diver]

@Wildranger Before you start pulling the head apart to swap the plugs. Grab a multimeter and check that the glow plug bus bar is geting a full twelve volts when you hold the key in the warmup position.