t.m.c.
    My gut feeling is you have not done any harm to your engine. The oil
pressure warning system/light is an on or off device. It is not an analog
device i.e. it was not designed to start dim and intensify. Most likely the
rain was shorting out.
    The only way to be sure is to test the oil; pressure with an analog
gauge or install a VDO gauge in the cockpit. See my web page.

Ken Lewis
http://neksiwel.20m.com/