By Dirk van Dijk of Zacks.comNEW YORK ( TheStreet) -- In September, home prices continued to slip, and the declines were very widespread. The Case-Schiller Composite 10 City index (C-10) fell 0.67% on a seasonally adjusted basis, and is up just 1.52% from a year ago. The broader Composite 20 City index (which includes the cities in the C-10) fell by 0.80% on the month and is up 0.55% from a year ago. In August, the year-over-year gains were 2.50% for the C-10 and 1.61% for the C-20, so it looks like the year-over-year gains are rolling over. Of the 20 cities, only one (Washington DC, and it was only up 0.05%) posted a gain on the month, while 19 saw prices fall. Year over year, five metro areas saw gains and 15 suffered losses. In August, there were also 19 down and just one up. It thus looks like a new downtrend in housing prices is under way.