You get TR3 at auto parts stores. I've never had it mess up decals. On a machine with a compromised clear coat I'm careful about the decals, use very light pressure with cotton balls.
What to use for cleaning/polishing a machine is a personal choice. Up to now I've always used TR3, but all the machines I've done have been from the 50s and 60s. It's made my black 301, my 201-2 and my fw so shiny. I imagine I'll use sm oil, at least at first, on the New Home treadle when I start cleaning it up.
Cari