Black Tank Gate Valve Leak

Came back in from camping last weekend and when trying to dump the tanks, I opened the black tank valve and .......nothing...... I'm thinking "Oh ****..." sorry for the pun :B) ...there's a pyramid. So I go inside with a flashlight and open the toilet flush valve to see...well, I'll spare everyone the graphic description... So, with the water hose connected to the flush valve I begin to run water and get only water out of the sewer hose. So, with another water hose I go into the coach, hold open the flush valve and have the DW spray a jet stream directly into the tank... and finally get results out of the sewer hose. So, after flushing and flushing and flushing both directly through the flush ball valve inside and through the flush connection in the wet bay...I've got the pyramid cleared. After dumping the grey tank, I mix up my coctail of Dawn and Calgon and 2 gallons of hot water to put in the clean tank, shut everything up and go about my business for the next few days. Mid-week, I noticed a small wet spot under the wet bay and on closer inspection, I noticed that it was Dawn and lavender-scented Calgon.....Ughhhh...now I know why the black tank wouldn't empty.....the liquid had dripped out under the coach onto the ground in the campsite. YUCK! :S There was no obvious indication of the leak at the campsite when I disconnected everything, (not full hook-up....state campground), but I really hate that it had dripped onto the ground there.

With that said and explained (sorry for the long write-up)....is there anything short of replacing the valve that is a potential fix? Could there be something stuck on the gate valve that isn't letting it close all the way? Gaskets gone bad? ???

All this to say...I really hate it happened and leaked onto the ground at the campsite, but hopefully no harm was done. I don't think any solids came out....