I've gone through 3 pairs of Bilstein B6 front struts in the span of around 2.5 years with my 2006 MR. I have never tracked the car, but it is my daily driver and I log 10-15k miles per year. I'm wondering if this abysmal failure rate is due to incompatibility of the stock springs and top-mounts with the B6? I also notice that the car is about an inch higher with the B6, compared to when it had the stock MR struts. Does the B6 strut need a different top mount, which would transfer more weight onto the springs?

No, the top mount is not what causing the strut to fail. The spring and dampner work together and a key component of keeping the strut from being damaged is the bump stop. If you drive over a pot hole the bump stop will prevent the suspension strut rod from crashing into the strut housing. Replace the bump stops and inspect the top mount.

If the top mount is bad it will create a knocking sound when driving over bumps. A bad top mount will be literally falling to pieces because the rubber in between the steel will wear out.

Thanks for this advice! The 3 sets of B6 I went through never came with bump stops, and I don't know where the OEM bump stops went, if they existed. I'm sure what happened is that the bump stops got lost. Do you know if it is possible to buy just the bump stops from Mitsubishi, if I get a new set of B6 struts? OEM bump stops should work with the B6 since the B6 also fits the OEM top mount, right?

Yes you can buy the parts from the dealership. I believe they should be available since its the same part on the Evo X.

Part number for Front Bump Stop - MR510136 : https://stmtuned.com/products/front-...em-evo-7-8-9-x
Part number for Front strut Dust Boot - 4060A646 : https://stmtuned.com/products/front-...em-evo-7-8-9-x

The Dust Boot keeps water and debris from going into the strut.

The rear suspension uses more rubber components. Luckily STM lists most of the parts on the website but they are missing two parts. : https://stmtuned.com/collections/evo...spension-parts

Rear Strut Top Hat - 4140A513 : https://stmtuned.com/products/rear-s...em-evo-7-8-9-x
Rear strut bushing - MR594613 : https://stmtuned.com/products/mr5946...spring-bushing
Rear Strut Pad - MB809280
Rear Strut Cup Cover - MB809281 : https://stmtuned.com/products/rear-s...-oem-evo-7-8-9
Rear Strut Bump Stop - MN100476 : https://stmtuned.com/products/rear-s...-oem-evo-7-8-9
Rear Strut Dust Boot - MB809284

hey man, thanks so much for the links! After looking at them, I realize that my oem dust boot was transferred by the shop to the B6. However the bump stops were not. The dust boot doesn’t resemble anything like what I imagined. They look like just a smooth plastic ring, while other cars’ dust boots look like a tubular accordion

no bump stop = damaged struts/shock . Even quicker whne the car is lowered more than 1 inch.. These cars dont have much travel on the struts/shocks to start with.
Get the bump stops installed. Hopefully the struts/shocks have not been damaged. already.