If you can clean out that via (left side of cap) it should be a straightforward fix. Thread a short length of #30 wirewrap wire down through the via and tack it to one side of a replacement cap. Be sure to remove the remains of the old cap lead on the right pad!
The area around UD8 and UE8 seems particularly prone to trace damage on SE/30 boards. It's hard to tell (may be lighting), but there appears to be corrosion on the pins of those chips. Highly recommended to remove them for inspection. You could also start by checking point to point with...
Unlike a lot of older machines, the Nextstation (Greyscale) '040 does not have an external switch to select between twisted pair and BNC connector. Is it autosensing, or is there a parameter or jumper change required?
I find it's much simpler and safer to remove the entire "top" (load) assembly before accessing the heads. There's a great video on YouTube that walks through faking a diskette load to collapse the loader, disconnecting tension coil springs on the sides and lifting it clear.
Did you recap the analog board as well? If so you may have inadvertently broken the vertical circuitry. In particular, examine the height pot and surrounding area.
Earlier this week I did the same thing to one of my SuperDrive mechanisms. After a bit of shameful language, I realized the little coil spring inside the head assembly had several notches available to increase head pressure. Moving it up to the next (higher) position was enough to do the trick...
I've found a post that outlines the default video mode in great detail. What I'm curious about is if the machine pays attention to sense signals from the monitor such that alternate resolutions are possible. The 13W3 connector carries signals for this purpose.