Do This Part Fit Sport Suspension, "BMW 335is"

Yes.

I have a 2008 535xi, some steering noise at low speeds loading and unloading and a few forums, as well as trying to locate the sound in my engine bay led me to believe this part could be the cause. My question, do I need to replace my strut when I replace this part or can I replace this part and see if that fixes? then if not, replace strut. Just trying to budget, thanks!

You don't need to replace the strut at the same time as replacing a suspected worn-out strut mount. However, the inverse is usually the case because a worn strut can cause excessive wear and tear on the strut mount and strut bearing.

Do I need to also replace the washer, gasket and nuts when replacing this? Are any of these included?

No additional parts are included with this mount. At minimum the self-locking nuts that secure the mount to the chassis are required replacements, p/n 31316769731.

How are you supposed to tighten the nut onto the new assembly if you're supposed to use a 6 or 7mm hex to stop the strut from spinning?

You would use the appropriate size strut nut socket. Generally a 21mm or 22mm 6 point. We offer CTA 3039X05 (21mm) and CTA-3039X06 (22mm) to torque the nut to spec.

Does this come with the three locking nuts to secure it to the strut tower?

Locking nuts are not included. Please see p/n 07119905374 for the locking nuts.

Does this part have any difference with part LEM-3121101 except price?

The difference is whether your car has the Sport Suspension or not.

How is this part different than part 31306775098?

Lemforder 2700101 cross references directly with BMW part number 31306775098 which means physically it's the same part. If you are asking how the Lemforder is different from the Genuine BMW part there isn't any difference to note of as the Genuine part is made by Lemforder.

Is this sold as a pair or one?

This strut mount is sold and priced individually. The same mount is use for the front left and front right position however.