Using the solution on SF StackExchange here here I have created a Workflow Rule and Field Update to show the value of a custom field present on the OppProduct Level in Opportunity Level (as that field needs to searchable in global searches)
The problem is that if there are 2 or more products only the most recent value of the custom field in the latest product is shown on the Opportunity level - Not both!
Is there a way to show all of them on the Opportunity field (maybe separated with a ;)