First of all, I'd like to thank the forum for the advice that I got with respect to the slipping clutch. Cdn$3,000 later, it's all fixed and the clutch isn't slipping. I also had all of the parts recommended in the parts list replaced. As well, the drive shaft and swing arm bearings were shot, so those were replaced too.
Now, a month or two later, I'm noticing some oil weeping around the rear boot (see pics). It wasn't leaking before I took it to the shop. Seeing as the rear transmission seal's been replaced, I don't suspect it. Any ideas as to what it could be before I go back to the shop to complain?
This type / location of oil leak can come from 2 places:
(1) the transmission output shaft SEAL where the drive-shaft engages into transmission (from of swing-arm). This has been changed in your parts list as item 28 (seal 25 x 40 x 6) although for some reason your dealer used the old part number and not the current one.
When this SEAL leaks, it permits gearbox-oil to drive dowm slowly by gravity into swing-arm (small angle going down when parked) and eventually accumulates near the rubber boot.
I have seen cases where the seal was either: (a) damaged during installation OR (b) inserted just 1 mm too far and will cause leak because of design of shaft (there is a small hole in shaft just behind this seal).
(2) the other possiblity is the Pinion seal of the rear-drive - this is just where the drive-shaft connect into rear drive (lowest point and farthest rear of swing-arm). In general this seal is NOT replaced during a clutch job unless they see a leak from there when removing the rear-drive. Part number "33 11 7 665 838" Seal 35x47x7. So if the previous one above is not the cause of the leak, you might just be unlucky and this rear-drive seal failed a few weeks / months after the did their work on clutch.
As posted in reply of H96669, this one may weep / leak very slowly just to create a bit of a mess without any major dripping. Check the fluid level of rear drive (lower thread of filling plug) and adjust if needed - fix it when time and budget allows.
IMPORTANT: Transmission uses same type / grade of oil as rear-drive so one cannot tell if leak comes from either by smell or color. The only way to be 100% sure is to remove rear-drive from swing arm and inspect if oil is present as far up into swing-arm (going toward upper swing-arm). Oil would have a hard time climbing up if it leaked only from lower rear-drive seal (pinion seal as my option 2 above).