A month ago replaced valve cover gaskets and all glow plugs. Gaskets were bad and all glow plugs ohm'd OK, but replaced them anyway. Was somewhat curious so today disassembled a few of the glow plugs and they all had oil inside them.

Is this normal, I wouldn't think so?
Overtime maybe the seals break down?

Here is a picture where the top of the glow plug is removed ...



Here is another one. More oil in there than the picture shows ...



Here is one with the shaft removed and cleaned with the seals slid down a bit.
One on the left is the oil seal, I think.
Bigger one on the right is the electrical insulator ...

 

That is strange Jim. You wouldn't think there should be oil inside them.

 

Jim I think they do have oil in them, not sure why. I did a Birthday video a few months ago. I thought it was interesting but some didn't see any value in it. the link to the thread is below. You comments about oil made me think of this video.
https://www.ford-trucks.com/forums/1...lug-video.html

 

Rich, I didn't see that thread before, interesting. Believe why the current goes down in time is because the GP has two wires in it.

1. The regulating coil which is the item in picture #3 above. It has a plus temperature coefficient which means as the plug heats up its resistance increases limiting the current to the heating coil.

2. The heating coil, the tip, has a zero temperature coefficient which means the resistance remains constant as the current flows through it.

My guess is the plug that did not work probably had a short at the connection of those two items (to ground), but just a guess. By the way I did the same on all the other glow plugs and all had oil in them, some more than others.

In any case reps sent because it was very informative video.