I have a 92 Subaru Loyale manual trans 4WD w/ ~200,000 miles & leaky engine but has been very drivable (mechanics agree). A week ago I first experienced a loss of acceleration power in 1st & 2nd gear combined with a loud knocking/clunking sound while turning right. Loss of power has occurred a handful of additional times since (frequently in reverse) combined with knocking sometimes and also sometimes back-end fishtailing/loss of traction. Knocking/clunking sound is intermittent (mostly not there). Sound slows and speeds up. Sound has always occurred while driving, but sometimes continues while idling. I just noticed drive belts probably need replacing. Would that resolve problem? Or is it something else?

Oil's full and clean and recently changed, coolant's full, no immediately visible cracks/breaks under car (axles) or under hood. Engine oil appears to be the only leak (mechanic diagnosed as typical old Subaru head gasket leak.) Different mechanic fixed minor coolant hose leak 1 month ago & assessed vehicle as A-ok.