Turntable dust covers protect the mechanism well, but are often killed or badly injured in active service. This was certainly the case for my Dual 505, which was rather tatty, scratched with a big crack in the side.
A cracked lid is very difficult to repair well. It requires specialist chemicals, skill and an element of luck. Mine ran out. I had a cracked lid from a 505 deluxe case which I transplanted my deck into for a while. A local perspex fabrication firm glued it as best they could and after a good polish it looked ok, but the cracks were still clearly visible.
Scratches are a different matter altogether. Polishing and lots of elbow grease can work wonders here. A badly scratched example will need to be tackled with various grades of wet and dry paper before polishing with a liquid abrasive and finally ordinary furniture polish. Some advocate use of products intended for refurbishment of car headlights. I have had good results with Brasso as a liquid abrasive.
When building a new plinth, sourcing a decent lid was a key factor. New lids can be had, but they don’t come cheap, starting at around £50. It is possible to commission a bespoke lid from a fabricator, but these start at about £60, even for something very basic.
I ended up going down the 2nd hand route. Two lids were considered for my plinth. A clear one from a Rotel , or tinted lid from a budget Dual turntable.
I posted a couple of photos on Facebook and the tinted one was universally preferred. It was in very good condition with only minor scratches. It polished up well with Brasso as the following photo shows. The left side is untouched. The right side has had just a couple of minutes work.
Left untouched, Right polished with Brasso
HiFi manufacturers know that the lid can make a massive difference to the cosmetic presentation of a turntable. In the 70’s an entrepreneur got himself ahead of the game by investing in tooling so that he could have his lids injection moulded in China. This cheap, but high quality mass production allowed him to under cut his competitors. The brand was Amstrad and the entrepreneur Lord Sugar.