Just because glow plugs were replaced a year or two ago doesn't mean one, two or all aren't bad again. Some lesser brands don't last that long, and with the systems that keep them glowing for a couple of minutes after startup they seem to burn out faster.
Many threads to search for on how to check this.

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John