Christine Cato wrote:
We have a leak in our roof and/ or box gutters and have been having
roofers come out to give us estimates. I'm not sure I trust all of the
information they are giving us though so if someone can tell me...

You can't do research on roofing contractors from the comfort of your
house. Get references, go take a look at their work and call some of
their customers. Ask for references from recently completed work as
well as some work that is at least a few years old.

Find out how the contractor works the roof. Walking on a slate roof is
one way to damage it. The contractor working on your roof should be
using hook ladders which hook over the ridge and distribute the weight
of the worker and materials over a greater area. If the guy doesn't
use a hook ladder the odds are good that he will damage good slate as
he's repairing the other things. Your gutter work shouldn't really
require the guys to work up on the roof as they're primarily dealing
with the lower few feet, but the guy's approach to the basics is very
important in sizing up potential contractors.

- Do slate roofs need regular maintenance beyond replacing broken/
missing slates?

No. You don't want stuff growing on the roof, so that obviously needs
to be cleaned off. The roof needs to be inspected regularly. One of
the issues with a slate roof is that, depending on the type of slate
used, the deterioration starts underneath the top layer of slate, so
it's not always easy to determine the condition visually.

Is applying a waterproofer or conditioner a good idea?

Not necessary, and it can cause more harm than good.

- Our box gutters definitely need to be relined. What is the correct
way/ material to use? Does the bottom row of slate need to be removed/
replaced to do this correctly?

Copper with mechanically interlocked and soldered seams. At least one
row of slate has to be removed. If you're in a cold climate it's a
good opportunity to remove the first few courses and install some Ice &
Water Shield to prevent ice dams. Some slate roofers consider the
membrane an insult to their craftsmanship ("Our roofs don't leak, so we
don't need no steenkin' membranes!") - I disagree with this stance. If
your house is perfectly insulated and perfectly ventilated, you
probably can do away with the membrane. Hint: your house isn't
perfectly insulated and perfectly ventilated.

We have gotten different info from different roofers, so I am just trying
to figure out what's best. Thanks!

Here're some links to help you do your homework:
http://www.slateroofers.org/
http://www.jenkinsslate.com/neanderthal.htm
http://www.cr.nps.gov/hps/tps/briefs/brief29.htm

R