A few issues quickly emerged when the gas company showed up, first the meters were in the basement when they should of been installed outside (legacy issue), second there was a small amount of leakage in the wall where the service came into the basement before the meters.Luckly since the leak was before the meter they took the responsibility of installing a whole new service from the street and putting all the meters outside.

CO detectors don't always go off if you start having some exhaust leakage into the home either.

Is there any sign of leakage?

If you install a second peace of plywood or particle board on top of the first one.angle it out and then cover the surface with lino etc as instructed any water leakage will run out and the tenant will become aware that the sink is leaking before the cabinet rots.

Is this signs of roof leakage, and if it is how easy is this to fix?

Signs of leakage?

Call local utility company for leakage tests.  

And I don't like the leakage involved with the sale of my house.2) Hold current house and use equity to buy 2 SFR or a single MFR REI, outside the state where my dollar will get me properties that will cash flow more readily than here in Portland.

Even if you remove the tank make sure you get a soil test to ensure no leakage.  

We received some heavy rainfall this past winter, and now I have leakage around my chimney.