I've done the lower oil cooler hose, but don't remember having particular trouble with 10mm bolts. I do remember that they are all strategically located in hard-to-reach areas, for no apparent reason. I think I used either two small 10mm combination wrenches (or allen wrenches -- but I could be confusing that job with tranny oil cooler lines), and lots of swearing words.

To detach the hose from the oil filter housing you absolutely have to apply a counterhold on the hex nut that's between the hose and the filter housing. I was too lazy to run to the store to buy sufficiently large combination wrenches, so I used two adjustable wrenches, which is usually a bad idea, but got it done for me that time. I did have to use a handle extension (ideally that would be a piece of pipe, but I used large lug wrench) to get enough leverage though. Before you do this, do yourself a favor and disconnect all vacuum lines in the area, or be prepared to replace some -- you can guess how I know.