Merc impregnator spray stained hood

[nap27]

Have used this several times with good results
This weekend the can started foaming part way through - hoped foam would then dry ok bit has dried white staining good badly
Tried nail brush and washing also hoovering when dry no luck - phoned merc and they have offered to collect car and clean hood but before I do that any suggestions ?

 

[WDB124066]

Maybe leave that one to Mercedes, unless by some miracle if you re-apply will it work properly...??