Hate to see unanswered questions! That's my thought.
If the surround is removable, haul it outside and coat it with stripper containing methylene chloride which will remove even the most obdurate coating given time and application. Remove residue with old newspapers/rags which can be disposed of.
Warning! Elderly people with heart conditions need exercise caution using MC by wearing appropriate protective gear (organic cartridge respirator). The primary transmission is through rapid evaporation, which is why outdoors or positive flow ventilation is required.
The treated surface may have some blotchiness. This sounds in order with your closing comment. If not, post again.