Oil, rim valve hole, rubber disintegration

Ti ~12 year old Specialized Ground Control

Oil source: leaky shock fork. Oil has been dripping out from under the
shock boot and down the left fork leg for the past several years (~4 to 5
years?). Oil reached the hub and flowed along the spokes to the rims. Most
of the oil flow probably happened over a short period of time and the flow
probably decreased or stopped after enough oil was lost. Before I cleaned
up the fork and wheel this past week, a thick layer of dirt and oil covered
the fork leg and front hub, with a lesser layer on the hub-facing side of
the rim. (Yes, I haven't cleaned this bike in years, but I just overhauled
the hubs yesterday...)The rim sidewalls were relatively clean being swept by
the brake pads. The plastic rim strip covered the spoke holes well, but the
valve hole was open to the oil covered hub-facing side of the rim.

The first two photos are from one side of the tire, the next two are from
the other side. The black patch is where the damage is. The yellow gum
rubber (?) is absent from those patches, and when back lit, you can see
light between the nylon threads of the casing. (Sorry, no back lit photos,
my camera's LCD is broken and I can't adjust the settings very well.) The
oil probably got to this part of the tire by flowing down the presta valve
of the tube to the interior of the tire. The rest of the tire is pretty
dirty and has evidence of oil on the outer "skinwall" part, but it is more
of a diffuse damage.

http://img200.imageshack.us/img200/7500/img25659fq.jpg

http://img200.imageshack.us/img200/5199/img25660ky.jpg

http://img200.imageshack.us/img200/5817/img25685hx.jpg

http://img200.imageshack.us/img200/9366/img25698mt.jpg

How did I happen to notice this damage? Well, the tube just suddenly went
flat on me yesterday and when I inspected the tube, I found the leak at the
valve base. Then I remembered the Carl/Jobst/Mark discussion on this topic
a few weeks ago. The tube is a Performance branded tube with one patch on
it. It has been on the bike for years - I don't remember my last flat on
this bike, and I haven't lived near a Performance shop in over 6 years. It
is possible that this is a defective tube, but it has already survived many
years. I haven't had to use a frame pump on this bike in many years, so it
wasn't bad pumping technique (I've never damaged a tube using a frame pump
anyway). I really can't say if the tube was defective or if oil weakened
the tube. Maybe it was a combination of those factors. Here is the tube:

http://img200.imageshack.us/img200/3103/img25705yb.jpg