NEW DUST COVER CARE AND CLEANING

It is more a question of your cleaning tools and techniques than product. Clean microfiber, straight lines, no circular motions. Just remove loose dust with a swiffer before anything. There’s a lot of info on cleaning plexiglass on the net. 

@2112oracle I don't have a dust cover on my turntable.  But for all other plexiglass products (screen in the car, plexiglass faceplate on the instrument cluster in the car, etc.) I use a product called Plexus.  It is made specifically for plexiglass and provides anti-static properties on the finished product, as well.  Available on Amazon.  Superior outcome to all other products of this category that I have tried.

As others have stated, use only with a clean microfiber cloth.  Clean cloth is the magic sauce for an excellent result.

I'm like a sponge,thanks folks.

Throw it out

@stringreen , and I suppose you wear your underwear for a week. Proper dust covers certainly keep dust off delicate mechanical devices and mounted correcting to an isolated turntable closed dust covers actually IMPROVE the performance of a system by attenuating the sound that gets to the cartridge by up to 10 dB. That is cutting the volume in half. 

Can dust covers decrease sound quality? Sure,  if mounted directly to the same chassis the tonearm and platter are on it can make like a musical instrument. In order to work well the dust cover has to have thick walls at least 1/8 inch and it has to be hinged to something that is not the chassis that the tonearm and platter are mounted to. Examples of turntables that have properly isolated dust covers are; the AR XA, some Thorens tables, Sotas, and the Kuzma Stabi M. 

You can have a dust cover made for any turntable then hinge it to a base the turntable sits on and you are in business.