In my opinion the drive in seals work just fine they are expensive but work. I’ve had many clam shell 021,023,025’s apart along with the 029-039’s. Not a ton of value in a ms250 they are 299$ new up here so if it’s in good shape with good compression and just has leaky seals I’d have no issue using the drive in seals. Lots of people aren’t going to dump 150$ into a 299$ saw there is a reason Stihl sells the drive in style seals. And if your going to pull it down to crank and do it right might as well do bearings also with rings but then you might as well buy a new saw. I also trust the old oem bearings more than a new set of china ones. If I remember the drive ins are about 40$ a set and they change out just like doing a pro saw. Make sure it’s not the impulse line sucking air and it needs the seals for sure. I’ve used the drive ins more than once and the saws are still going after 2-3 years. Was the only way it was worth it to fix them to the owners.