When you use E-junkie buttons, we pass a return URL to PayPal checkout which would override any Auto Return URL in your PayPal account settings for that checkout. Thus, the PayPal-provided buttons on your obd2.ca site would continue to use the Auto Return URL in your PayPal account settings, while your E-junkie buttons on carplugs.com would be returned to the URL we specify. However, note that where you set Auto Return: ON in your PayPal profile settings, you must also set Payment Data Transfer: ON as well, to remain compatible with E-junkie.