91 Accord speed sensor issues, questions

I have a 91 Accord with 160K on it. I've read through past messages to
know it is very likely I have a VSS problem, which happens to Honda's
about this time frame.

My problem is intermittent. The speedometer and odometer die, but the
tach does not. The blinking S light starts and is followed shortly
thereafter by the Check Engine light. Cycling the ignition resets
whatever sensor is causing this, but the problem returns.

It happens at a very specific temperature range. When the car is cold
or has been driven for about 30 mins, the problem does not occur.

My questions are:

I see speed sensors sold as two different items. One appears to be
just the electronics and is sold for about $50. The other has gearing
(hydraulics?) on it and sells for about $150.

Which should I replace? Both? Which is part #P4018-57994?

Should I wait for complete failure of the sensor to replace it? It's
hard to diagnose as is since it is intermittent.

Also, hparts.com does not appear to be a functioning website. I seem
to recall I looked at their site a year ago and it was just as
unusable as today. Is there a comparable online dealer for parts?

 

There's an overhaul procudures for the VSS. I
Google across a site that does. Here take a look, http://snipurl.com/arx6

 

The VSS is about $50, but the reliable steering speed sensor is about $150.