Got an answer from XC SEO... the code should be without the / after php.
<a href="manufacturers.php?manufacturerid={$products[product].manufacturerid}">{$products[product].manufacturer}</a>
I got this mod to work on both search.php and the products.php. But for product.php (not products.php) I used this code:
<a href="manufacturers.php?manufacturerid={$product.m anufacturerid}">{$manufacturer.manufacturer}</a>