A lot of people say leather boots last longer if you oil them with an oil like Lexol Leather Conditioner. (Concept: oil lubricates the fibers to make the leather pliable enough not to crack, and slows rot.) I'm told this is one of several factors that can extend boot lifetime by a factor of several.

But Lexol says not to oil suede or nubuck leather with it, to use a lighter oil. Experimentally, if you add oil to suede, it absorbs a lot, turns very dark, and the nap goes down.

The problem is, I'm not sure how to get oil past the suede lining into the main leather part. The boot is too thick to just oil the outside, and I'm not sure much oil would get past the top polish anyway.

There are a number of suede "cleaner/conditioners", but they mostly seem to be surfactant (detergent), which might remove oil rather than add it.

Any ideas for proper maintenance?

While I'm at it, should I do anything about sheepskin tongue linings?