Several years ago I ordered a spacer for my Valmet from the importer here in the US. It is a black piece of vinyl 10" long by 5/8" by 3/8" thick. It is concave on the 5/8" sides and veed on the 3/8" sides. You just press it in the gap and it stays. Doesn't look too bad either. If I remember I thought it was a little pricey at the time although if memory sreves it was less than $30