You could consider doing one AutoRX trial. See
www.autorx.com and the Additives forum of
www.bobistheoilguy.com
This product is only available frm their website. It rejuvenates the seals, cleans the combustion chamber and ring packs, and reduces the potential for leaks.
I used it two years ago when I switched from dino oil to full synthetic and liked the results.
Otherwise, just do a drain and fill and forget about it.