I agree with a previous post - you may be jumping to a premature
conclusion. Lets work on the oil issue. If your oil appears too thin - that may be the reason your oil pressure light comes on!
Have you put any additives in the oil - does it smell like gas(diesel)?
I'll assume you've run the engine up to operating temperature with your suspected gasket leak. If you are getting water in the oil
it will generally be the color of peanut butter - with the consistency of the previously mentioned milk shake.
In order to get a good look at the oil - I suggest you drain the pan
and take a good look and smell it! Does it smell like anti-freeze?
If not - replace the oil and filter and breath a sigh of relief!
You don't say what viscosity oil your using - or if it appeared to be thinner after reaching operating temperature.
Now to the leak - are there any hoses (hidden) going thru the
cowl supplying the heater core? Also you dont say how much fluid
is leaking. Does it leak constantly - or only when the motor runs?
I've seen cases (especially in cold weather) where older cars will
weep fluid between the head block connection. Also -just occured to me, could there be a freeze plug back where your leaking fluid.
Maybe a rusted freeze plug is causing your leak.