Whiteline KSB751 Diff Front Support Lock bushing.
Fits all WRX/STI 93-07 and foresters etc.

Fitted it, loved the improved feel of the rear end but it was too noisy for my liking when combined with all the other super stiff mounts I already have on my subi, so had them taken out after a lap around the ASG block

$40 is your bargain, available now, pm.

"KSB751 will reduce rear-end float particularly under acceleration. It will also remove drive train slap on hard gear changes while delivering more precise handling & chassis response from the rear."

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06 STi: 337hp @23psi on E85...
06 STi: 309hp @22psi on 98ron...