[Boatanchors] Beam antenna question

[RAY FRIESS]

Need some advice from the fellow old timers here ... or even the wise newcomers...

I have a HyGain beam antenna, the Explorer 14.   Fairly old, but has been a great performer with nearly unity SWR from one end of the band the other on 10, 15 and 20 ..
until recently.
 
Now, a few weeks ago the SWR on 15  shot up so high that it nearly pins the SWR meter.   However, the SWR on 20 and 10 are still less than
1 to 1 and it continues to load fine.   Barely moves the needle on the SWR meter.
 
My question is, what should I suspect?    A 15 meter trap gone bad, or maybe corrosion in the area where the traps and elements are clamped together?
The antenna has been up for about five or six years now, without any trouble prior to now.   Sometimes there would be brief periods of a few hours with a
high SWR such as when we had snow accumulate on it, but when it dried up, the SWR came back down to normal.
 
I thought if it was either a bad trap or a corroded element to trap joint that the SWR would be all out of kilter on all three bands, not just 15 meters.
 
I'm sure it's something with the antenna.   I use a TS-50 solid state rig with the automatic antenna tuner.  It still loads and puts out full power on 20 and 10,
but on 15 because the SWR is so high, the power dips down to about 5 watts output on the beam.   I can load a regular dipole without problems. 
I tried taking the auto tuner out of line to see if it was having a problem on 15, but I still get the same high SWR without it in line.