Fly Line Question

I purchased an Orvis Wonderline, WF-5-F, 3 to 4 years ago. Paid about
$50-$60 for it. When I started cleaning and conditioning the line
this year I found th following condition:

The first 4-5 yards of the line was in excellent shape. However the
next 4-5 yards, where the diameter of the line increases
significantly, the line was discolored, grayish, and there appeared to
be small cracks. Upon inspection with a magnifying glass, I could not
detect cracks. The rest of the "thick" part of the line entirely to
the end, where it tapers again, appears fine. I fish mostly the White
River Vermont watershed where the water is somewhat acidic. I
probably average 2 times per week fishing. Also, I clean and
condition every year.

Any ideas what the cause of this condition might be? Maybe it's time
for a new line? The performance still seems ok.