mgdg & richfaa,
It's a Material problem. The stock ones are a poor quality imported steel. The shackles are stamped mild steel. I know you can replace them with the same from a lot of different places, but you will have the same problem again.
The Kit comming from Dexter are thicker shackles and are probably a higher quality steel. When I get them in hand I can verify this. They do not looked stamped. The other thing is they are fitted with zerk fittings so they will accept grease. You also get bronze bushings instead of plastic.
The Worlds best Steel came from the US, but as you know most of that industry has gone overseas. We traded lower price for lower quality. Even if the new ones are the same quality steel you will be riding on a larger lubricated surface area which will extend the life many, many, times even with a low quality steel.
mgdg, actually if the quality is as good as it looks it's a bargin, at $89.
You can see them at
www.easternmarine.com
Happy Camping