/OK, I understand now, thanks.
The newer 20-30s use a plastic driveshaft tube with an oring on either end, I haven’t seen a real problem with them though. A good overheat can surely melt the plastic tubes though. The small gearcase 9.5 and 10hps had an aluminum driveshaft tube with orings, the only problem I have ever seen with those is just being left out during assembly.
The 9.9/15s don’t have an actual removable driveshaft tube. The short shaft models seal up inside the exhaust housing with that large oring around the top of the impeller housing. The long shaft models have an additional plastic tube that fits snugly into the top of the extension housing, the white plastic tube fits snugly up into the exhaust housing as well, there are no orings used on the white plastic tube.
Your picture shows a 9.9/15 driveshaft with quite a bit a salt build up in the upper spline area, you were lucky to get that apart without a fight! The driveshaft oring is missing, which usually just results in accelerated spline wear, your splines (driveshaft at least) look OK. I am wondering why you have pulled the lower crankcase seal head though, again you were lucky to get those three bolts out! I’m thinking that a missing impeller housing seal/oring/plastic spacer might have allowed excess water up to the spline area. Keep in mind that there is usually a little drain hole in the exhaust housing that ensures water won’t just fill up the driveshaft tube, perhaps this hole is plugged up with crud/barnacles.
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