Search with site - odd.

Any text I include in "Store/ Detailed" Description can be found using a search on the site. However I am trying to get rid of plain text and go to custom items. However, when I make the manufacturers part number a custom item instead of plain text it cannot be used as a search key within the site.

So for example one product I sell has a manufacturer product code 188159 and many of our customers would be likely to punch this in as it is written on the product. It does not form part of the Store Display Name. I have also noticed that numerical "Display Names and "Supplier Name" do not work in the search box unless you append an alphanumeric such as a space. It does not even work with "Store/Search Keywords" if the search tern is a numeric part number!