Chiefjim writes:

Curious to learn - what is a realistic life expectancy for a garage flush mounted fluorescent light fixture?

Discovered to my dismay that all three fixtures were dim and
flickering. The house itself is 40 years old but the fixtures appear
to be 10-20 years old based on the press fit connectors used. Garage
is neither heated or cooled. Temps here can be teens in the winter to
over 100 in the summer.

For florescents, that sounds like normal aging.

When I went to test whether the tubes were good I discovered a
tombstone very stiff. So stiff I was afraid I might break the tube
trying to put it in. Even the original tube balked at going back in.
In the process I also managed to snap a mounting tab from the
tombstone. Do these become brittle over time?

Yes they do. But they are easily replaceable.

Original intent was to put in new tubes if that was all that was
needed. If ballasts were bad I considered reconfiguring for led's.
But if the tombstones need to be replaced it seems maybe replacing the
entire fixture with one designed for led's would make sense.

Interesting. I have the LEDs on order, and I plan to install
the LED tubes in an existing fixture. Today I took the fixtures apart
and found one socket (not tombstone) was missing a chunk.

Since the new LED tubes are single end I know one socket just has to
hold the bulb in place, so I may or may not order a new socket.

Looks like new sockets are easy to identify and order.

With that final thought in mind. Assuming a standard junction box is
hidden by the existing fixture would a square or round flush mount
ceiling light be a viable alternative? Say something like this?
http://www.homedepot.com/p/Commercia...3141/206589815

It's "home repair", not "home replace".

--
Dan Espen