How much would a new gas (lp) manifold cost on a 2011 E 310?
Who would have them? I know Weber should but any others? I can't seam to find just the manifold listed.
Weber has lots of parts that they don't list on their web site. You have to call them and ask.
Someone listed a "conversion kit" for a Weber in Chicago CL which probably includes the manifold, hose and regulator. It might fit your grill as well. Edit: Here is the listing. http://chicago.craigslist.org/nwc/hsh/2686796434.html
There are other vendors on the net that sell Weber parts as well as some sellers on eBay.
I'm not aware of anyone third parties that make that kind of part for Weber grills. I have seen grates and flavorizer bars though.
