Internals are not the same but look similar but wired differently on the circuit board
They perform completely different tasks. The pin in pin out connections are the same that's why it fits . It's cheaper for the manufacture to have a standard base cover and connector and just change the internals to the task at hand and stick a cheap part number label on the outside for identification.
There is a lot of information on the forum on this relay problem even guys much cleverer than me that have add parts to the old relays to fix the original problem.
I just bite the bullet and replaced with new.