NEVER use actual base cleaner on your bases (even the Swix tech reps will tell you the same). Base cleaner should really be called "kick wax remover" for Classic X-Country skis. If you use it on glide wax areas, it actually removes the glide wax that has penetrated and conditioned your bases, thus making your bases slow.
To clean your bases, you should do a hot scrape. Melt on some cheap wax, iron it over the base, let it sit for a minute, then scrape it off. It will pull out the dirt from your bases but not remove the wax that has penetrated and conditioned your base.