tommo 01fos

hi guys..... i'm looking for some help.
my manifold on my 2001 forester s-turbo has been blowing for a bit now, and on closer inspection i found that the egt sensor in the up pipe to the turbo is loose. (sliding in and out ). i removed the sensor but it seems fine, its like there is a bit missing from inside the hole in the manifold that the sensor should sit against. the car has had an after market stainless manifold fitted before i bought it and ive no paperwork about it,so cant ask the supplier.
can anybody offer any advice please