The r/h shifter is not returning after shifting up to the larger cogs. Do I need a new return spring, or maybe just gummed up? Thanks

First thing's first. Tri-Flow the crap out of it. If that doesn't work then maybe it's time for a new spring.

Also replace the shifter cable. The wrap at the brifter tends to cause older cable to take a shape and then begin to fray.

I have had very little experience with brifters. That said, I had success with a Shimano 600 lever that didn't want to return/downshift. First, I removed the lever from the body. Then I flushed the lever with WD-40 while working over a small plastic tray to collect the extra WD-40. When I had enough run-off WD-40 to submerge the top portion of the lever in the corner of the tray, I left the lever submerged in WD-40 for a few hours, or maybe overnight. Then I let it drip dry, and soaked it in Mobile 1 synthetic oil for a few more hours, dripped dry again and wiped clean, then reassembled.

Here's a nice photo driven how-to (may be slightly different for a Dura-Ace brifter):

https://imgur.com/a/0tPBK

I thought I was going to need to try a full service, but all I needed was to get rid of the old gummed-up grease (soaking in WD-40) and add fresh oil. Worked like a charm.

My 1st guess is that all the above may be unnecessary, but it depends on the speeds.

Older brifters have a return spring on the top front of the body, under the cap, and it often comes out of it's slot, resulting in poor "returns." Simply taking it apart, and re-inserting the spring (under tension) will solve that issue, if that's the cause. The majority of the time, it is. Be careful taking it apart, and have a place where dropped stuff can land and not get lost.