I think there are three things that may give off a soapy flavor; One, beer that stays on the yeast to long in the fermenter can give off a soapy flavor. Two, improper rinsing of you equipment (kegs, fermenters) can leave an alkaline contamination. Three, I think I once read that old hops may also give a beer a soapy flavor, although I'm not sure about that one. I don't know if any thing can be done about it. I doubt it will ever get better or go away. I would focus on your keg washing procedures first and make sure the kegs are being well rinsed. On the other hand, being an Old Ale, they tend to set around a while, sometimes on the yeast to long.