Oh Lord! "Sticky!" Ha-Ha!
Odds are that the original spill was not such a big deal.
The cleaning afterwards likely had the effect of spreading the sticky soda into the fan bearings and allowing it coat some internals with goo.
This coating may be causing some components to run hotter that they should, causing throttling issues. The fans are probably less effective now. (if they're contaminated)
Putting the new GPU into your PC will probably fix your problems, but if your original GPU still runs, albeit in a less efficient state, it can probably be returned to full functionality with the proper cleaning, and drying methods.
Don't toss it, & don't give it away.
Look into giving it a proper cleaning and then you'll have two GPUs to run in SLI (combined mode) for much better performance than one alone can give.
SLI's performance is much better than a single card. It's worth it to do.