18 years; Sudden gimp in hind leg comes and goes
So my 18 year old Norwegian Forest cat has suddenly developed a strange gimp in his hind leg. He's pretty healthy for his age, still spry and limber with an average weight.
He gets around just fine but at random times he will yell out in pain followed by the inability to put any pressure on his left hind leg. After a few minutes it goes away and he's fine until the next episode. It happens sometimes when he's just laying around or when he's active, about 5 times these past two weeks. I've put pressure on and around his leg/back to see if I could get a reaction but I get none. He also urinated outside the litter box which never happens (clear and plentiful). Not sure if that's related but it's strange none the less. Bowel movements seem to be regular, but I could be wrong on that front.
Any ideas? Thanks in advance.