I am sure there will be peeps out there with much better intel than me, but the way I tried to rescue mine was:
1). Do not use ANY fluids, as I was told during my apprenticeship in printing that age softens the emulsions used in both negs/slides (colloids?).
2). Use a VERY soft brush (I used a sable hair artists brush) to remove any surface dust.
3). Wipe VERY softly with a soft cloth such as that you would use for spectacles (I have a 'selvet' cloth from my printing days, but a proprietary lens cloth from any camera shop should be ok).
Hope this helps, and I will not be offended if anyone shoots me down.
Best regards and luck