It may have had grease on the springs, or it may have been an adhesive that has not aged gracefully. Does it feel/behave significantly "rougher" or "worse" since being taken apart and cleaned of this yellow substance?

I would recommend using silicone based oil or grease instead of this yellow stuff (which is probably standard bearing grease). This is the best imho, very thick and works great on all plastics:

+1 for silicone grease. Works wonderfully for almost every plastic application and don't mess rubber parts.

As a kid I washed MX310 and added a drop of grease afterwards. Within a week the wheel was completely covered in it. Ew.

I use paraffin for bike chains, the last lubrication lasted 350km. It's dry and washes off easily, so the chances of getting it where you'd rather not have it are zero.

These scroll wheels were very dirty and there were dirt also in the spring that presses against the inside of the scroll wheel. So I don't really know how it should feel when scrolling. Compared to the other mouse that I cleaned, this seems to be a little quieter.

The other mouse I cleaned is similar to this picture below. The scroll wheel is a bit rougher to use with this one. I'm not sure if I should buy any lubricant, because it easier collects debris and I don't even really need these mouses for real use. Just picked these from a recycling bin at my workplace because wanted to see if these can be fixed.

But I'm also now sure that the silicone grease would be the best option if applying anything to these.