Sounds to me like it could be the defective capacitor on the ICU
See:
http://www.g2ic.com/forums/showthread.php?t=127170
http://www.g2ic.com/forums/showthread.php?mode=hybrid&t=56089
photos:
http://www.imagestation.com/album/pictures.html?id=4290425277&mode=guest

Mine (91 teg) was bad and caused random chirping and eventually no
intermittent wipers. They work now and no more chirping.

The oil sensor is on that circuit because if the pressure drops for a
certain amount of time and then goes above the threshold value the ICU will
flash the light until you turn off the car in case you missed it when it was
actually low (or something like that, can't quite remember, but I just
verified in the wiring diagram that the pressure indicator is wired through
the ICU).

It's cheap to fix it yourself (I replaced the original 100µF, 16V, 105C cap.
with a 100µF, 35V, 85C from RadioShack for a $1 or so), but it's a pain to
remove the ICU.

Also, mechanical gauges have a pipe fitting thread (it is tapered) so it
snugs up somewhere in the middle. I can't say for sure whether you have the
right size, but when I was installing one in an Audi and I thought the same
thing as you. I torqued it down a bit and it seems fine. I used teflon tape,
but don't use excessive amounts that could tear off and clog things up.

--Art

I've searched this group for previous messages and noticed that the oil
pressure light has been mentioned a few times. When it's been raining for a
long time it comes on, flickers, or is real dim. In addition the headlight
chime also chirps randomly during the same weather conditions. I never knew
that the chime even existed because it doesn't work as it's supposed to.
I've replaced the oil sending switch and problem still exists. Tried
connecting a mechanical oil guage to test pressure but am having problems
finding right fitting for block connection. Standard 1/8 inch thread only
turns in about 1 1/2 turns and I don't want to force it any further.
There seems to be a Technical Service Bulletin # 90013 called "Engine- Low
Oil Pressure Light Flashes". Can anyone tell me what this bulletin is about?
Any help greatly appreciated.
Kindest Regards,
Robin