Search for some of my posts on reusing and replenishing selenium toner. I have working solutions that have been going for more than 10 years. Just filter out the precipitate, replenish with a bit of stock to get the level of activity you need and you should be good to go.
That said, if your toner dilution was rather weak to start with and there's a definite precipitate, the amount of selenium in solution is probably next to nothing. Discard and start over if a test indicates no toning activity.
Doremus