hello brick lovers!

I have read all about the warnings and the consequences of failing to do a scheduled timing belt (TB) service on the 850s and S/V70s--nearly scared me to death! I have never bothered to consider a TB service on my '89 240 because I thought it didn't apply to older cars. I've been reading around and am getting concerned. My car has about 188k on the odo, and I don't know when was the last TB service. I understand that the 850 has a 70k TB service interval. So, based on that, my car should have had a TB service done at around 140k, and the next TB should be done at 210. Hmmm, or is it a 50k interval for our beloved 240s? My car has 188k right now. How do I know when was the last time my car has had a TB service? Is there a sticker somewhere, as there is on the 850 and S/V70 cars? I don't remember if it is indicated on the service manual; I'll check on that tomorrow. Just supposed I have NO CLUE when the last TB service was performed. Is it a wise choice to get that done asap? If yes, what should I expect from my Volvo shop, like what will they do (I don't want to be short changed by not having something done that is a part of a TB service). On average, how much is a TB service? I live in the west coast. Thanks!