copied from:
https://68kmla.org/forums/index.php?/topic/27238-estimate-looking-at-possibly-replacing-mainboard-in-future/
I'm looking at your SE board and except or the rust, it looks OK. Wash the board out with ammonia and distilled water and then rinse it with a high proof alcohol, and it should be fine for years.
The SE Board is robust, it can take a serious beating. But is is not an SE\30 with a more powerful and faster CPU, FPU, and able to hold more RAM,
but caps are not going to explode on you like an SE\30. The SE as its place in the Vintage Mac arena. I would love to have one but for now I don't as I do not have the money to get one.
Except for the dirt and rust on the metal frame, this should be fine after a good wash and rinse down. Blow Dry with a hair dryer or compressed air.
The rest of the case should be as dirty, so it should be cleaned out as well. The Rust you can deal with some rust remover or rust paint and paint over it. This machine should out last you if you take care of it right.
Adding to it:
How is the rest of the metal frame inside the case? Any rust on that metal? I forget which member who it was, but an exploded battery damaged the metal case on an SE, SE\30, Classic or Classic II, but the logic board was recoverable. The rust on the metal frame was taken cared off with steel wool and then painted over with Rust Neutralizing paint. It gave the frame a luscious black finish.
EDIT:
Good that it can boot from the internal High Density Drive. Now you can get high density disks for it and format it to make a larger boot disk.