A faulty gearbox can cause the water to spill over the top, I calnt remember exactly how it causes it but i can remember having water spilling over the top and I tried everything to cure it before whirlpool technical advised me on the gearbox fault, changed it and all was ok, i have had a couple the same since.
Chay
I have just had one leaking from tub on spin; the outer tub had a small spilt in it near the top.
The balance weight that sits on the top of the tub had come lose and had cut a split in the tub. I just patched it.
With the cabinet off you would see it. Just had a look on Whirlpool CD and there is a gasket listed it goes on the top (Part No. 481946669993) never had to fit one though.