My Heil 7000 furnace, installed new in 1993, is leaving a wet spot on the floor just below the lower right panel edge. When I slide my finger along this lower right edge, there is accumulated water, which is dripping ever so slowly, causing the wet spot. What might be the cause of this never before moisture production?

Sounds like you might have a leaking condensation line leaking or its stopped up,either way its got to be fixed before you get water damage to the furnace