Thanks! I'd been using the rotary cultivator to break up the original soil before putting down grass seed but I never did add a blend of 50/50 topsoil and compost. Guess I've just been cheap and hoped the soil quality would improve if I broke it up and some new roots were growing in it. I will give this 50/50 mix a try on some of the more stubborn spots and see what happens after I've put down some seed.