The option to "place the masking salve" is missing from the options.

Out of all the many things that need to be collected, in order to cast Merien's spell, this is the one that is NOT an item in the house.

The player was supposed to receive it (I don't know if it was ever an inventory item, or not) from Dame Clarique, after talking to Tamien Sellan. Whether you go off and help some villagers, or use Persuasion to get her to free Tamien immediately, you are supposed to automatically have it, before entering the Sellan residence.

You then have to pick up all the other things (the glass gems, ritual candle and shrouding ashes) and learn the incantation, which is conveniently told to you in a nearby scroll.

Then you go to the spell table. Recite the incantation. Get the option to place the four things and have to remember which order to do them in.

BUT, the option to place the Masking Salve is missing. (Despite the fact that you should have received said bottle from Dame Clarique earlier: it is impossible to get to this stage without having gone through the process that should result in you getting it). Only THREE options were there, and all of them are wrong. (Candle, Glass gems, Shrouding ashes.)

This makes it impossible to progress the quest any further.

This is a change that has happened in the last 3 days (because 3 days ago, on a different character, I was able to complete the quest: the option to place the masking salve was there.)