There is a lot of dodgy fuel line out there.
Every now & then I come across a mower where the owner has used either neoprene ( goes soft & sticky ) or PVC goes hard & shrinks.
Glad to hear you are out in the yard again.
If you feel like it put a match to the end of the old fuel line.
If it starts to burn it is most likely PVC.
If it is genuine Buytl rubber it should char & check.