Unless you can pinpoint your engine oil leak to something specific, I’d go for the rocker cover gasket even if you don’t think it’s that. I had a leak for a year after doing timing belt etc around lower LHS of engine and rear and thought I’d damaged the crankshaft seal doing the work - eventually went for the rocker cover gasket and hey presto, oil leak fixed.
Having done my rocker gasket three times on my car now, and given poor fit of new ones, if the gasket isn’t particularly old or damaged I’d reuse the old one (it should have stretched a bit to be a better fit) but make sure you seal it into the rocker cover with a suitable sealant (e.g. Loctite ) and let it set before assembling, and use more sealant (automotive silicon seal worked for me) on the mating face to the head. Make sure all faces are really clean after disassembly and before assembly.
Others may disagree ref re-using the gasket but I found new ones are invariably too short and difficult to get to stay in place. Obviously if there is damage / hardening of the old gasket it will have to be replaced.
