I have an old 3 speed bike with 26 X 1 3/8 wheels that I've ridden for about 25 years. Just recently it has developed a creaking/squeaking sound coming from crankset. I've oiled the crankset but after 30 minutes or so of riding, the squeaking resumes. What can I do to remedy this? Should the crankset be greased and not oiled?

I've also tried to find out what brand of bike this is. The markings on it include a label on the headset that says "Mark 2" and the word "Monterey" on the chain guard.

Thanks,

john