Complex sentence: Continuing the servicing of GN's, they produced their own car based on the Austin Seven, but the venture was unsuccessful, with only about 10 cars produced by the time the company ceased trading in 1928.
Split into simpler sentences: Continuing the servicing of GN's, they produced their own car based on the Austin Seven. However, the venture proved unsuccessful, with only about 10 cars produced by the time the company ceased trading in 1928.