Shifting into second

Had the old girl out for a decent cruise today up to Calabogie and back, about 250km. Yes, Calabogie is a name of a real place not something I made up. Theres a real nice stretch of hwy 511 getting there all full of twists and hills. Mostly the old Twin performed like a champ however...

About half way home it started refusing to shift into second. If you mashed on it enough and hard enough it would get there and then sometimes pop out again so more mashing, hurting toe. Got it home alright but I was constantly calculating every time I had to stop just how long it would take me to get home in first gear.

I'm guessing it's got to do with the interlock gizmo that prevents you from shifting into second when it's stopped. I'm also guessing someone here has seen this before.

Make sure the clutch is working right.
Steve

Every other shift up or down is smooth as glass. Only first to second is wonky and not always.

Could be a weak return spring or bent large shifting fork.
Steve