Hello
After testing Wavelab LE8 version (8.0.3) on both Windows 7 and OSX 10.9 Mavericks, I have found that Wavelab LE 8 does not currently support the Mp3 Upgrade Patch. However if you purchased from the shop account the list of Steinberg compatible software never includes Wavelab (LE), it only mentions Wavelab Elements. I do understand the confusion but if you need that list you can find it here.
http://www.steinberg.net/en/shop/buy_product/sku/500242444.html