i kind feel like an idiot for never noticing this, but for those of you who might be having trouble clearing your cache. check to make sure your Steam Cloud Sync is turned OFF. recently noticed that when clearing my cache it was not working. after a bit of checking i found that my Steam Cloud Sync was turned on, which in turn would reload those cache files.
go to your steam library, right click on Mudrunner, open Properties and go to Updates tab. at the bottom turn Cloud Sync off.