I was out checking fluids and found my man transmission oil is a bit low. So i go to my handy Subaru Owner's Manual and it reads, among other things, that i shouldn't mix brands of gear oils. Thing is, i just want to top it off... but should i be worried and do a full fluid change? I've got < 9K miles on the car. I do think it strange that the fluid's low, but there are many historic posts i can read on that topic. Your thoughts? Thanks in advance.