Starter Recommendations

Folks,

I am having a problem with hard starting on my 1968 235 C ( O540 - B4B5 ). The starter will not drive the prop past the first instance of TDC consistently. In order to start my plane, I have to "rock" the starter back and forth with the ignition switch. First of all I would like to ask... Is this common?

The 230 HP Continental in the 182 I fly and the 310 HP Continental in the SR22 I have flown did not have any problem turning over the big 6 cylinders.

Assuming this is not a normal condition, does anyone have suggestions as to what we might look at to troubleshoot the problem? Also, I am looking for suggestions as to which starters work the best for this application if I have to replace it.

The plane had the starter and battery replaced in October 2005.