1995 Buick leSabre custom

Passenger rear subframe bushings rusted
out. Tried to replace them with Dorman
parts Dorman number 924-043. Sub frame
keeps slipping right through the bottom
bushing to the bottom bolt causing both
bushings to touch. I called General Motors
and they say you need the vin number to
clarify which bushings you need. I'm thinking
the Dorman kit that I bought just wasn't the
right size has anybody else had a problem
like this?
I'm also thinking because my motor is a 3.6
that's too heavy for the Dorman bushings
and I just need original GM parts.
Anyone got advice I'd really appreciate it.