[MBZ] glow plugs

[Luther Gulseth]

Checked the glow plugs on my CD and mom/dad's '85 300D tonight.  D  
readings were open, 2.6, 2.6, 2.6, 2.6.  Ordering a set for that car for  
sure.  Mine were 3.3, 3.3, 3.3, 5.0, 4.9.  Do glow plugs gradually  
increase in resistance as they age?  Or do they stay the same, then  
suddenly short/open out?  This is the question I need to have answered.

--
Luther  KB5QHU
Alma, Ark
'83 300SD (happily running WVO/diesel mix)
'82 300CD (Slate grey, black MBTex, WVO/D mix)
'82 300D '90 300E (both parts or can run??)