Very stupid question, but how long does it last. Installing new prop this weekend and I have a bottle that is 2 years old. Does it get to the point where it is less effective. Probably a telling point is if it looks to liquidy.

Again, sorry for a stupid question when the stuff only cost $7.

Use it. Should be fine.

I would say if it was dry and hard if its still in liquid form I would use it as long as its not running

if it's still wet, just stir it up good.
if it's dry I add some wd40 to it and stir it up good.

I'm still using what I got while working at a nuke in 76. As Dead Animal mentioned add some WD40 or lube if drying out. I have three types, copper based, nickle based and aluminum based. My Son's and my work force hated that I insisted it be used on flanges and bolts on High Pressure Steam. But go back a year later and the gasket falls right out after being in service. Now the one Son is running a big job and he makes his guy's use it as well. I guess they learned something from the old man.

This applies.

I've got a can of nickel that belonged to my grandad. My dad told me as a young boy that two drops of that shit would cover three counties. It wasn't until I was making my own living turning wrenches that his phrase made sense.

For what it's worth, if you buy another jar of it, the marine grade is well worth the extra money....just speaking from experience and from a guy that changes out props on a frequent basis.