Im not sure the reason behind the macs muffler thingy but I.I.R.C. its been discussed here somewhere before and I think it was pretty much a non issue . Perhaps someone else could chime in here . If you want to see goop , try the norvel as a coincidence I was flying mine yesterday on a scanner and its turning that plane to poop not goop pretty quick . Doesnt help when the covering is layered into the wind so any breeze and crud is being forced under the covering and the printed on covering is turning brittle and yellowing at the rate of knots . Still like the engine though and I clean the plane between flights which you may have to do to help if its a problem but a well sealed muffler has gotta help . The norvel uses castor but I would use a good quality synthetic like stihl hp ultra etc. As for the price , well its good value to me . Would hate to go through all that rooting around and expense and then find I was still up ****e creek anyway . Cheers the pope