Shortly after leaving home in my '87 Buick Le Sabre, it shiftly fine
into first gear, but when shifting into second, seemed to suddenly go
into neutral.  I had to ride in first gear at 15 MPH to get it
anywhere.  When back at home, fluid was checked; level was OK and fluid
did not smell burned. The trans. fluid and filter were changed one year
and 8,000 miles ago, but we decided to change everything again.  There
was quite a bit of metal shavings on the magnet in the pan, and the
filter looked very dirty.  After the change, we took the car for a test
drive.  It seemed to do quite well until we had driven long enough to
warm it up, then the same thing happened again with second gear.  It
almost seems to be a temperature issue.  The car has approx. 118,000
miles.  Is the entire transmission shot, or could it be an individual
part or problem we have overlooked?  We replaced the vaccum modulator
and the vaccum lines were checked out before the test drive.