well...with the studdering.. Try a solid copper antenna, that might help. With clones, the range is completely different for each car, it seems. The 3 clones that i played with at a shop of same brand, make, and frequency had ranges that were completely different.
for the turning radius, it seems like your magnet or your magnetic coils are not alligned so there is an even amount of space between them when the magnet is centered. If you open the front end up (carefully! remember where all the pieces go) most people with a lick of sense can spot a problem. Try looking through
www.ausmicro.com ...they have pics of opening front ends.