Topband: Insulator problems

[Greg - ZL3IX]

The Tx antenna I have been using very successfully for the last 8+ 
years, is a top-fed vertical.  This feed arrangement requires the yagi 
used for top loading to be insulated from the mast.  I have been using a 
nylon insert between the two halves of the stub mast as my insulator.  
This morning I noticed high SWR, firstly only on high power, but then at 
any power level.

Today I brought the mast down for inspection, and the only sign of 
trouble I can see is in the insulator, which has bubbled visibly. This 
may (or may not) be the problem, but I propose to change the insulator 
even if only to eliminate it as the culprit.  I have a couple of 
questions for this group.

1)  Does anyone know if I can upload a jpg file to contesting.com, so 
that guys can see what I am talking about?  Tree, I guess I can't attach 
a photo to a post to the group?
2)  I always thought that nylon was a pretty good dielectric, and did 
not expect problems, especially at 1.8 MHz.  The gap in the insulator is 
7.5mm, or about 0.3".  I estimate that there will be around 2 kV across 
this gap.  Is nylon perhaps not as good as I thought it was?
3)  If I replace the nylon with Teflon, will I lose anything in 
mechanical strength?

Unfortunately this problem means that I will not be able to enter the 
Stew.  We are going away for a week for the festive season, next 
weekend, so won't have time to fix the issue.

Comments welcome.

73, Greg, ZL3IX