Question concerning my 1976 300D; Engine 617.91; Body 115.114. To Quote my engine service manual Job 15.4 505/16 "If the engine is not started when the preglow indicator lamp is extinguished, the preglow system remains switched on up to 90+20 seconds of preglow time. When working in engine compartment, note that in such a case the resistance conductors are red hot."

My Question: I changed the 5 glow plugs this September with new ones (Bosch). I noticed at that time that the conductors in fact did turn red hot. Now 3 months later the conductors get hot but do not turn red. Are my plugs going bad after only 3 months?