as said it can really be night n day when it comes to the difference ,
and rember not all aftermarket panels are mate in the same place , weve had italian ones , chineese and jobbies made in tiwan ,
a panel beater worth his salt could make a aftermarket panel fit and look spot on ,
granted if budget allows and there available id say go gen , but in current times there either way overpriced of just not available ,
as for how long it will last , any panel gen or not will only last to the same extent as how its prepped n fitted and how the cars looked after ,
me and karl have been working on a s2 that had sills fitted , cant be that old , as the sticker inside was like new , but it had rot to bits as when they fitted it they bare metal'd there areas to weld and never protected the areas ,
99% its all down to shoddy workmanship ,
beef