This is all very moot Digi.

A copy is ok for personal use if it remains in the owner of the original's possession and is not offered for sale.

Is this sale for a Vinyl LP and a Remastered CD or is it for a Vinyl LP only (with a CD thrown in)?

In other words, is ownership simply being transferred at no cost.

Would it also be illegal if the seller gave the buyer details of the remastering setup so the new owner could DIY?

It's probably a technical breach of copyright but this would keep a bevy of lawyers quite busy and a judge may be inclined to let it slide in judgement (depending on the condition of his liver lol).

Does the CD constitute an original work in it's own right as the OP has expended time and effort to remaster the original?

There have been a few cases in recent years to do with music sampling that seem to point this way.

If there is a breach here it is so minor one would wonder what the fuss was a about.

Just rework the listing to avoid naughty words and everyone should be happy.