Mr. t. For your motor mount or small bits in general... What I have done and will continue to do is clean off the existing rust (a small, brass wire brush will do) and apply a very
light coat of corrosion protector. I think, I'm currently using this: https://www.nocorrosion.com/
although I have used light oils, in the past. I tend to apply the stuff with a small brush, in most cases, in that it minimizes overspray and uncoated areas. Careful getting too much on the rubber motor in the mount.
You might try using WD-40 as a cleaning solvent in lieu of 409 on occasion.
Just re-read your post and failed to address your manifold rust. Mr. H's suggestion is a good one.