I bought a Stihl 029 in 1995 or so, was my one and only saw used it tons. The plastic handle cracked but that was my fault. About 8 years ago my boss had a much newer 029 that his son in law ran straight gas in, cooked it. I put my motor into the MS290 case which meant I got flip caps (best thing)!! But its still the motor from 1995, and still running today. Saw can sit all summer in the basement with ethanol free gas in it, take it out in the fall, 3-5 pulls she's running like a champ, every year. As a back up to my 029/ MS290, I bought a MS390 thinking I needed a bigger saw, & it was, but I was mostly disappointed with the saw, it would run 20" bar ok I guess, but anything longer, or a less than perfect chain it just didn't have the oomph to go through hardwoods. I found my self running the 029/MS290 all the time anyway. I did appreciate the compression release though when starting the MS390. Recently I bought a lightly used MS361 PRO saw and after running it the first time, I sold the MS390 and am not missing it at all. So my unprofessional opinion is, if your 029 is about to be retired and even if its occasional use, go with the MS261 PRO saw, you will not be disappointed, more power, and less weight than the 290, yeah its more $$ but you won't ever think to yourself, should have went a little bigger. I would not even consider the MS390 as an option, a couple more lbs, but not enough power to justify the weight & extra size.
Besides some of us might need your 029 for parts someday!!