I remember many years ago reading a comic in which a one-appearance (or at any rate, obscure) character with transmutation powers turns Wolverine's claws to wobbly rubber. Wolverine, who had been in middle of rashly lashing out with a stab, hears an unexpected "B-BOING!" as his claws harmless bounce off the target of his rage, and I think maybe even says, stunned, "'B-boing'?!?" ⎩O⌓o⎭
The transmuter character later restores them to adamantium. (I think he wasn't a villain, just some decent guy who had been blackmailed by an actual villain that if he didn't help, someone close to him would be harmed, or something like that.)
This is arguably in contradiction to the later event in X-Men #25 in 1993 (during the "Fatal Attractions" storyline) when Magneto ripped out the adamantium, which led to the reveal they actually had had natural bone in them all along.
The following could be wrong, but I vaguely recall that it might have been in a comic in which Wolverine didn't usually appear, like Excalibur. This would have had to have been in an early '90s comic or earlier (i.e. before "Fatal Attractions").