Does your W use her car to transport your son? If so, I don't think it hurts doing mainteance on your W car. And since it's something you have always done it won't be pursuit. You are also the man of your house and that shouldnt change because of your Waywardness.
Oh, and you don't have to tell her you did those things. Just see if she notices. Just do, them and go about your life as usual.
M:37 W:37 T:11 M:10 S17, S13, S10, S4 BD:06/28/17 OM confirmed 07/20/17 Recon the M 10/29/17 Working hard:2gether
Onward and forward
This process is not a sprint it's a marathon! Patience, Patience, Patience.