Crack on outside wall

[ScottishGasMan]

got this crack under the window sill outside the house, wandering if there's any advice as to what to look out for in future or if it's likely to need attention, don't remember seeing it a year ago, but the sand stone render had been reworked a few years ago and possibly was masking it.

House is about 100 years old, solid stone/sandstone walls,

 

[^woody^]

It looks like some sort of movement has gone on. Is there any sign of movement further to the left or right of the frame?

I'd fill it with a clear silicone, or a (non- acrylic) mastic of similar colour to keep the water out, and monitor it for a year over the seasons

 

[ScottishGasMan]

No visible signs of any movement an where else, no other cracks anywhere. But as I say they redid some of the sandstone finish just as I bought the house so it may have been there for 50 years and it's just the finish that's showing it through now. Will seal it as said and keep an eye on it over the summer.

Thanks