Yes, file the motion. Document the "themes" of your issues with your son's mother -- ie. alienation, missed visits, if she's told another man he's his "real" dad, etc. My husband took his ex to court last month on a contempt motion and while by a law an evidentiary hearing must be held before a finding of contempt in our state, the judge said there was no question there had been contempt and told Mom to expect to go to jail the day of the evidentiary hearing. In fact, he repeated that statement. My husband made an agreement for make up time w/his ex and let her off the hook for contempt, though many ppl said he should have let her go to jail. It's a fine line AND a lot more expense and would have likely alienated his last of 4 children even more. The child is in counseling with Dad. She's a great kid, but also very much alienated. It's so dang sad what some CPs will do to their children. I am also a CP and should "have every right" as some ppl might say to mess with my ex b/c of the thing he did in past years, but I could just never make my children self hate by tearing him down. He's not as involved as I would be, I could just never live as far as he does from them, etc., but he is doing the best he can and I just can't make my kids question who they are, where they come from, etc. by putting them in the middle.
Anyway, the counseling is imperative, I think, though a 13yo may feel freaky going. But, if you find his feelings are often confused and just parroting Mom's feelings, I think it's important to have a place to talk about things and also for you to not feel castrated being a parent which also means being the "bad guy" sometimes, too. When CPs alienate kids, I think the NCP feels like they have to walk on eggshells and never say "boo" to the kid and that's really not doing them favors, either.
Good luck with your motion. Are you going PRO SE?