I agree with harka about the hormonal problem. Take your pet to the vet right away to get the proper treatment.
What Could Be Making My Dog Smell Bad And Loose Hair?
It could be dying. Sad.....
Improper diet could be making his fur fall out. Whether is be in certain spot or overall shedding. Like to much protein will give them hot spots. It will lose hair and be irritating to his skin with out any visual skin problem besides the hair loss. The smell if coming mostly from the dogs ears will most likely be mites or dirty ear, if the smell is coming from his mouth it may be due to the fact the old teeth rot and then there gum get infected and or the other way around. Also I agree with harka with the hormonal problem that is a common problem with most older dogs. I hope this helps.
Simple make him smell your socks or shoes
This happened with one of my elderly dogs as well. If it is not a skin infection then it is most likely hormonal. Old glands do not work well, like everything else. Ask at the pet shop for a dog shampoo that is deodorising, and make sure to wash his bedding too.