I can't seem to stop a leak coming from the upper rear connection of my proportioning valve. This is the block that attaches directly to the inner fender and is the line that connects to the smaller block (see picture). All lines are new, block is original but looks fine. No matter what, I get a slow leak from that fitting only. I have tried loosening and retightning, rotating the line inside the block to try and seat it in, nothing is working. Is there any kind of sealer I can apply to the flare end to help here? Any help would be appreciated.