I noticed that my oil cooler is leaking onto the coolant hoses below, and just ordered all the necessary o-rings. The questions I have that don't seem to be addressed by the FAQ or searching old threads are:

1) does all the oil need to be drained from the car first? The oil was changed when I bought it, about 300 miles ago...

2) since it's only the o-ring at the rear of the cooler that's leaking, can I just replace that without having to remove the whole thing? Where it attaches to the block is spotless.

3) it that's the case, then do I have to detach the coolant hoses and drain the coolant from the car? Or is there enough room to keep everything in place and just get the new o-ring in? I'm planning on replacing these hoses anyway, but wanted to make sure the leak is actually fixed first, before possibly leaking oil onto brand-new hoses!

Thanks for any advice.