Crack in sandstone lintel

[Etch]

Hello

Due to the bad weather i have developed a two foot horizontal crack under the window in the lintel. Anyone advise what is the best medium to repair this. I was told not cement due to the reaction between sea air and cement will corrode the sandsotne.

What about outdoor polyfilla? or is there better?

 

[PrenticeBoyofDerry]

The crack is not effecting the structure of the building is it? if so suggest a replacement!
This stuff for remedial work, non cement product.
http://www.stone-tech.co.uk/stone-repair-mortar.html