Based on radar data, maps, and a possible known route, these are my conclusions:

Radar
    Looking at the known radar targets:
From "Norwood, Ma. (1,200 ft. @ 14:45 P.M.)"  to "Mansfield, Ma. (2,000 ft.)", then to "5 miles South of Taunton Airport (1,100 ft. @ 15:06:02)", then East to just North/East of South Middleborough, Ma. "lost radar contact (15:06:14)", then to last taget just West of "South Carver, Ma. (500 ft. @ 15:18:14)".
It isn't stated that "lost radar contact" (15:06:14) is a target on radar or not.
If it is a target, then the time difference between that location and that of "South Carver (500 ft. @ 15:18:14)", does not coincide.  Therefor, the "South Carver (500 ft. 15:18:14)" target, would not be Gerhard's plane.
If it is not a target, then the time difference between "5 miles South of Taunton Airport" and "South Carver (500 ft. @ 15:18:14)" may coincide between these two targets.  This would mean that the plane traveled from the target, "5 miles South of Taunton Airport (15:06:02)" to the target of "South Carver (15:18:14)".  Depending upon the speed of the plane and winds aloft, which are still being looked at.
Route
    Looking at Gerhard's Route:
Ironically, after placing Gerhard's route on a map and looking at it, it may appear that he may have been following railroad tracks that would have been visible out his window.  This can be seen on the following map (click here).   These sets of tracks run perfectly parallel to his route.
Aircraft Problems
After investigating and researching incidents and problems with this aircraft, there have been 2 known problems:
(1)  Airfilters  Air filters were recalled because of air filters deteriorating and causing small fragments to be ingested into the engine causing reduced or loss of engine power.  To view recall   (click here) then hit "back" on your browser to return to this page.
(2)  Wings   After reviewing some incident/accident reports regarding this type of aircraft, it has been noted that in some accidents the wings seem to be a factor.  A wing or wings may separate or come off during midflight operations.  This is caused by corrosion.
Summary
    If Gerhard were to be following the sets of railroad tracks as mentioned above, it wouldn't make much sense for him to go East all of a sudden.  Before even looking at the sets of tracks, it still didn't make sense to me that he would go East.  My assumption is when Gerhard went flying, he already knew his route or had it in the GPS.  At this time, I believe Gerhard was just going to take a flight around Marthas Vineyard or Cape Cod and back to Norwood.  If a straight line is drawn from Mansfield to "5 miles South of Taunton Airport", then beyond, it would go to Marthas Vineyard.  I believe he was using these railroad tracks as a guide to get him to the coast.  If this theory happens to be correct, I believe his plane maybe found on the western side of the railroad tracks between "5 miles South of Taunton Airport" and New Bedford Airport.
    If the witness reports in Danielson, Ct. are of Gerhard, he was definitely having engine trouble.  All reports in the Danielson area coincide with one another.  He was also seen in Thompson, Ct. which is North of Danielson.  He may have been attempting to make it to Jaffrey Airport in New Hampshire.  
Conclusion
East Scenario - South Carver, Plymouth & Manomet Area's
It appears to me, that if Gerhard had suddenly veered to the East, he would have been headed towards the coast.  At this time, he would have used up 1/2 an hour of fuel out of 2 hours of fuel.  That would leave him 1 hour of fuel left, taking in account the 1/2 hour of fuel for return.
If he had turned to the East, and the "lost radar contact" is a target, the area to be closely looked at, would be just North/East of South Middleboro on the Eastern side of  Rt. 495.  (Click Here) to view this area.
If the 500 ft. target is actually that of Gerhard, he was gradually losing altitude.  If Gerhard had a problem on board, I believe he would have called for Mayday if he was going in gradually.  My belief, is that something catastrophic happen on board in order for Gerhard not to radio anyone.  He may have been attempting to keep control of the plane in order not to crash.   This would mean he may have gone down very fast and nose in.  This would hamper search efforts by air as there would be a much less of a debris field.
South Scenerio - Freetown, Ma. Area South to New Bedford Regional
If Gerhard kept following the railroad tracks as described earlier, he may have gone down just West of Rt. 140 around Freetown, Ma..  (Click Here) to view this area.   I do not believe he would have gone much further than this point, as New Bedford Regional would have seen him.

Gerhard Home / Mansfield to Taunton Map / East Pictures / South Pictures