1971 Scamp

SCAMP.JPG Hi Everyone,
My son sold our 1973 Duster with the slant 6, he wanted an 8 and so many people told him not to spoil the old girl. We now have a 1971 Scamp (Sassy Green) with a 318 all stock. Just picked it up yesterday. A Canadian car always lived in the Okanagon Valley. It has sat for 3 years. Did a compression test today all cylinders between 135 - 150 except 2nd from rear passenger side at 100. Could this be a sticky valve from sitting ? I drove it home about 15 miles.
Any ideas would be appreciated.