One of my favourite methods removing glue residue from tapes is using another tape. It involves no solvents and thus cannot harm varnish.

I use to take some piece of tape, place it over the glue residue and pull it off. sometimes it is better to pull it fast, if the residue is rather hard. If the residue is soft, pulling gently may be better. I made the experience, that it doesn't make a big difference if you rub the tape onto the residue, or not. But the outcome may vary. You will have to do this several times, depending on the age of the residue.

I prefer to use duct tape, because its glue is soft and thick which lets it grab even irregularily shaped glue residuebut other tapes may work, too. Beware of cheap tapes as they sometimes loose their glue, worsening the situation.

A piece of tape may be used several times depending on its type and amount of dust on the surfaces.

One of my favourite methods removing glue residue from tapes is using another tape. It involves no solvents and thus cannot harm varnish.

I use to take some piece of tape, place it over the glue residue and pull it off. sometimes it is better to pull it fast, if the residue is rather hard. If the residue is soft, pulling gently may be better. I made the experience, that it doesn't make a big difference if you rub the tape onto the residue, or not. But the outcome may vary. You will have to do this several times, depending on the age of the residue.

I prefer to use duct tape, because its glue is soft and thick which lets it grab even irregularily shaped glue residuebut other tapes may work, too. Beware of cheap tapes as they sometimes loose their glue, worsening the situation.

A piece of tape may be used several times depending on its type and amount of dust on the surfaces.

If that doesn't help you can still try cleaners based on orange oil. Those have removed any tape residue I met! But be aware that orange oil is a powerful solvent, so test it on a covert spot. A brand available in a typical "Bioladen" is "AlmaWin"