I use a spray conditioner by McGuire (sp?) that appears to be quite
commonly available.  Can't complain.  The company is well known for it's
cleaning products... actually, I believe, they are the OEM for MB care products

cheers, guenter

Sun is leather's real enemy, IMHO.

Every few years I use Lexol Leather Cleaner and Lexol Leather
Conditioner on my cars' leather seats. (The cars are always garaged so
my leather's needs are modest.)

Someone who bought an old M-B whose leather was awful restored its
leather over several days, including (re)dyeing it with various
Leatherique products.  Tremendous improvement vs. "before" condition.

i would be cautious of leatherique... i have seen some awesome before
and after photos, but heard some bad stories about how durable the
recoated leather is... im talking about the multi-stage leatherique
process with the went sand, crack fill and redye.. looks fantastic, but
apparently it wears poorly

i have recently read some good stuff about neatsfoot oil, and that it
restores cardboard-like leather to its former glory, however i've also
read that today neatsfoot oil isn't actually neatsfoot oil, so be
careful here too! i am planning to try some out on my passenger seat
leather, which has for some reason become as stiff as cardboard while
the rest of the car is fine.. it's difficult to find though

at the moment though i use meguiars gold class leather condition cream..
it doesn't perform miracles but it does seem to work better than other
sprays and creams that i've tried

your best bet is to maintain the leather while it is new, rather than
waiting for it to get old and crap and then trying to turn back time!

Hello,

I use Neatsfoot oil on all things leather.  This is based on a
recomendation from an old leather craftsman in Tucson who told me that
many other products don't preserve leather because they leave the
leather dry.  He especially disliked silicone and petroleum based
products.  The best Neatsfoot oil is 100% pure, I pay about $18.00USD a
gallon at a store that sells horse saddles.

One needs to be careful not to over apply and to wait awhile (to let it
soak in) before sitting on the seats.

For more info:
http://en.wikipedia.org/wiki/Neatsfoot_oil

leatherique(.com)

No, 2-3 times a year.