I stuck it in the class
includes/classes/dynamic_price_updater.php

PHP Code:
$this->responseText['stock_quantity'] = $this->product_stock;
define('DPU_OUT_OF_STOCK_IMAGE''');//steve missing: https://www.zen-cart.com/showthread.php?70577-Dynamic-Price-Updater&p=1355225#post1355225
if (defined(DPU_OUT_OF_STOCK_IMAGE)) {