Keeping nylon and leather belts alive
Care advice fails when it treats all belts as one material. Ours are nylon webbing, elastic weave or leather over a steel-cored track, and each fails differently.
Nylon and elastic
Sweat and dust are the wear agents. Pull the strap out of the buckle, hand wash it in cool water with plain soap, and let it dry flat away from a radiator; heat is the one thing nylon webbing genuinely hates, it sets a curl into the strap. Do not machine wash a belt with the buckle attached, the buckle wins against the drum and against your other laundry.
On elastic weaves, check the leather tips once in a while. The weave outlives the tips; a drop of leather conditioner on the tips twice a year keeps them from drying out and lifting.
Leather over a ratchet track
Two rules. First, condition the outside like any leather: a thin coat of conditioner every few months, more if you live somewhere dry. Second, keep liquids away from the buckle slot. The track inside is metal and a spring; water that gets in drains slowly and sits against the mechanism. If the belt gets soaked, pop the strap out and stand both parts to dry separately overnight.
Trimming a cut-to-fit strap is part of care too: cut once, conservatively. A strap trimmed too short is scrap, one trimmed a bit long just hides an extra inch inside the buckle. Ours carry an 18-month warranty, and a bad trim is the one failure it cannot cover.
Buckle mechanisms
Ratchet and quick-release buckles want nothing but the occasional shake-out of pocket lint. No oil: oil holds grit, and grit is what actually wears a ratchet spring. If a release gets stiff, rinse the buckle alone in warm water, dry it, and it almost always frees up.