If you are already on the product page I assume you already have the product item and that product item should have a "ProductType" multilist field. You can use Sitecore.Data.Fields.MultilistFiled to avoid worrying about have to split the raw values.
You can then use Sitecore's Predicate Builder to build out your search predicate, which I assume you want to find all products that have one similar product type. You should adjust this search logic as needed. I am using the ObjectIndexerKey (see more here -> http://www.sitecore.net/Learn/Blogs/Technical-Blogs/Sitecore-7-Development-Team/Posts/2013/05/Sitecore-7-Predicate-Builder.aspx) to go after a named field, but you should build out a proper search model and actually define ProductTypes as a List< ID> or something similar. You may need to add other conditions to the search predicate as well such as path or templateid to limit your results. After that you can just execute the search and consume the results.
As far as Solr stripping the special characters, this is expected behavior based on the Analyzer used on the field. Sitecore and Solr will apply the proper query time analyzers to match things up so you shouldn't have to worry about formatting as long as the proper types are used.
var pred = PredicateBuilder.True<SearchResultItem>();
Sitecore.Data.Fields.MultilistField multilistField = Sitecore.Context.Item.Fields["ProductTypes"];
if (multilistField != null)
{
foreach (ID id in multilistField.TargetIDs)
{
pred = pred.Or(x => ((ID)x[(ObjectIndexerKey)"ProductType"]).Contains(id);
}
}
ISearchIndex _searchIndex = ContentSearchManager.GetIndex("sitecore_master_index"); // change to proper search index
using (var context = _searchIndex.CreateSearchContext())
{
var relatedProducts = context.GetQueryable<SearchResultItemModel>().Where(pred);
foreach(var relatedProduct in relatedProducts)
{
// do something here with search results
}
}