Spend a little now spend a lot later
As Rod says above you will need 8.33 soon and mode S is already with us so I would bite the bullet ans look at some new equipment, I would start with Trig or Garmin for your aircraft.
The TMK170 was a notoriously poor radio with frequent failures, I know of at least three people who spent more money getting these things fixed than buying them. No doubt someone here has the only trouble free TKM170 and loves the thing, but on the whole the lack of them within the industry tells a story.