In my CRM there's an activity where sales people assign a product manager to qualify and come up with the best product, service and solution for a particular sale.

The solution found here:

how-to-give-a-user-access-to-other-user-leads-opportunities-but-to-all-leads-opportunities-210078

won't work, because I only need product managers to be able to see the opportunities which they've been assigned on, not all those sales team oportunities.

Thanks in advance!