First thing WD40 will eat rubber. FACT
Second thing, on the internet only time tested theory is repeatedly given year after year. Yes some remain theory but this remains fact.
Third thing, not all rubber/lube/airsoft are created equal and for a hop-up to last a year with WD40 is not amazing. Minimal coverage and sitting time can slow the effects as well it may be that your hop rubber is less sensitive. But that is key, less, it will fail eventually and cannot be recomended for further use to anyone.