I have a 2000 Discovery with a chasis mounted 100 pound tank, It has liquid near the bottom of the tank near a brass plugm it is the odorizing liquid, why is it there???
A 15 YO tank will have some 'distillate' oil residue. If the tank is empty (no pressure) you can open that drain and reseal it with YELLOW teflon tape. Refill tank as normal and check for leaks.