I just measured my chain stretch for the first time and it exceeded my tools max measurement. So I bought a new SRAM PC830 chain and upon opening the box, discovered the sticky nature of factory grease. Which would be catastrophic for my dusty desert commute! So obviously, that has to come off. I consulted the web and found a brilliant website with charts for various chain lubes. https://zerofrictioncycling.com.au/
I ended up following KMC’s advice and cleaning the grease off with a light oil (WD-40 was handy). Then a wet lube (I forget the brand; whatever my LBS stocks).
OP said the chain was worse than the max measurement on the tool, but now I’m remembering that it’s just a pass/fail tool. At first I was thinking they meant their chain finally got replaced long after it should have.
The max measurement is when you swap chains.