Could this be a problem? Because my cylinder head and around the muffler has this yellow gold brown substance on it and it won't come off. This may be because of the heat but can this actually be a sign of a bad engine?

I talked to a guy at my local hobby shop, and he said my probelms with my engine always dying on me was because I was fiddeling with the mixture too much and that I am just to leave it alone at all times if I get the right signs if its the right mixture. Well, what if my engine keeps dying on me? Won't I need to adjust the mixture? This is why I keep fiddeling with it. I didn't know that it would be doing more damage to do so. Isn't that what its there for?

On my last flight when I said it was a deadstick, when I was bringing it down, I was running out of runway or field so I had a pretty hard landing that bent the front landing gear. This question is a little of the topic, but I wanted to bring it down before it would hit a gravel driveway that sloped up from the field I was using to takeoff and land. What I did was kinda pushed the airplane down so that it would land before the driveway because I was afraid it would do more damage but I had a pretty hard landing with a loud thump and bent the front landing gear. Should I have just completed a normal landing and let it land where it should rather than trying to force it back on the remaining field or did I do the right move? I really hope this didn't do any damage to my engine futher. Heres how bent the landing gear looks. Is it bad?