Oil on glow plug.

[Themgs14]

In the process of installing new glow plugs and injectors (currently in process now), one of my glow plugs had oil on it. So far all the others have only had carbon deposits. I am new to diesel, but with experience in gas, I would guess it is poorly sealing rings (1), bad valve seal or stem (2). Any input would be greatly appreciated. This vehicle is an 87' ford 6.9 ambulance w/ 100,000 on title and odometer, c6 trans. I cannot assume it was always well cared for but at one time fleet maintained.

Any help please,
Thanks.

P.S. having read through forums I did not come across this issue, if it is in here please direct me to location, and if I should post elsewhere please direct me as well.
Thanks Again.

 

[S-west]

I have oil on 2 glow plugs. Compression test came up with perfect compression. I couldn't figure it out but I'm kinda figuring valve seals.

 

[OLDBULL8]

As the glow plug is threaded in the head and goes directly into the precup, it's pretty hard to get any oil on them, the piston would have to push oil back thru a small hole in the precup. I would think you had some oil in the indent where the GP threads in.