The no-flushing advice really is meant for vehicles that have high miles and have never been flushed. In those cases, flushing CAN cause damage. If the fluid is red and doesn't smell burnt, you should be ok.

But it is really best to drop the pan and replace the filter. Read this post on pros can cons of flushing

People started saying that story about flushing an old transmission a long time ago. They forgot to stop saying it after it didn't cause any problems. If your car runs OK you might not need to flush the transmission. The filter catches all the particles that might do harm, so there's non of that floating around to clog up the transmission.

Flushing a transmission is better than just dropping the pan and changing the filter. Because the torque converter is still full of old nasty fluid. Some say to leave it alone and not service the tranny while others say to do it every 50,000 miles.

Many of us don't believe in "flushing" a transmission.....but follow the manufacturer's recommendation that for most car says to drain the transmission, remove the lower pan, change the filter, clean and replace the pan. A flushing doesn't change the filter, often doesn't change 100% of the fluid and many believe stirs-up debris rather than removes it. A lot of the quick-change lube stops that make a big profit flushing transmissions don't even carry all the different kinds of fluids used by various transmissions.

I waited a long time before taking a position on flushing. Some say it is associated with transmission failures because people bring failing transmissions in for a flush. But I have seen enough horror stories here of perfectly good transmissions failing soon after being flushed to take the position that flushing any transmission is very dangerous.

So I will quote top contributor, USAF hyd/pneu tech, and expert mechanic Holey Mufflers: "any trans that needs a flush should be disassembled, hand cleaned and inspected prior to rebuild. so either the trans needs new fluid, or it needs to be rebuilt. period! "

I have a 2000 Ford Ranger with 145,000 miles on it. At 74,000 miles and almost ten years ago, I had the transmission flushed and the filter replaced. Unfortunately, I did not stay on the usual 30,000 mile/2 yr. schedule for changing the fluid. Some people have said that flushing an old transmission may actually cause problems. The fluid still looks great and is a nice clear reddish/pink. The transmission also runs fine. Should I do it? I plan to keep the vehicle a couple more years.