from that Import Service magazine ...

Diesel No-Start
Diesel VW

Virtually all passenger car Diesels use glowplugs to provide
additional heat for starting, particularly in cold weather.
Glowplugs, of course, are just hot spots to ease the compressed air
mixture and the injected fuel those couple of extra degrees warmer to
reach the temperature of autoignition.  But they are not universally
interchangeable, even for the same vehicle.  Some glowplugs reach
their target temperature quickly, drawing heavily on the battery's
storage capacity to heat them quickly.  Others draw a lower current
for a longer period to reach the same heat.

The amount of time it takes to reach the autoignition temperature
depends on the temperature of the intake air, of course, but more than
any other factor, the engine combustion chamber wall temperature is
the deciding factor.  When the engine is shut off, the engine coolant
will correspond very closely to the temperature of the combustion
chamber walls, so that is the critical input.  Each Diesel car has a
glowplug control relay (or glowplug controller in the computer for
late-model vehicles) that determines the glow-time from the coolant
temperature.

You see the opportunies for problem here.  If someone puts the
short-duration/high-current glowplugs in a car with a long-duration
glowplug control relay, as long as the battery holds out you'll have
excellent starting for quite some time ... weeks or months, perhaps.
Then, since the business end of the glowplug is a metal thimble with a
heavy lamp filament on the inside, the glowplugs rapidly start to burn
out, just as the weather starts to cool if Murphy's Law comes into
play.  Not only are the glowplugs conducting more current and heat
than designed, so is the glowplug control relay, which races them to
see which burns out first.

Solution:
A no-start or intermittent-start Diesel with a history of burning out
glowplugs almost certainly has either the wrong glowplugs or the wrong
controller or both.  Don't replace either without confirming the parts
numbers of the other and comparing both numbers to what the carmaker
originally installed.  And don't let your customers be deceived by
claims of higher performance glowplugs that are merely repackaged
fast-burn units.