Hey, nice job on that SM custom. It looks like a real solid paint job. Just a little constructive criticism for you.
The red on Sentinel Maximus is more of a maroon. You did a great job with the other colors, so when missing the dark red it looks a little, no offense, unfinished.
There's a guy who may post here, but also posts at TFW2005. His name is Sculpt-Bot, and hand sculpts, casts, and does custom
Transformers heads. If you ever decide to tackle this project again you should contact him, as I bet he could get you a cast copy of SM head.
Again nice job, and good luck w/ your sale.