The use of these labels of Left/Right or Liberal/Conservative (Progressive/Regressive?) concerning Truth seems so childish and weird, and only useful in divisiveness.  Sorry, but it just makes me feel like I am in Wonderland. It takes us away from the essentials to deal with egos. One faith, one baptism: the best ecumenical movement is to end such labels and association (and, of course, do away with luther-, calvin-, and wesley-anything in our beliefs). 
There is one truth: one is either advancing that or not. Truth is neither liberal nor conservative. In fact, in spirit and truth such things are enemies of the soul.
The problem is impossible to solve for the attempts are trying to unite two different paradigms--and they are not compatible. The common ground is never going to be found in what we believe but in how we believe. How we believe is where spirit resides.