On my 2002 DL1000 I've had to replace the clutch slave cylinder and I've installed a Werks basket. So I've seen the innards on both sides.
Due to extensive research beforehand, here are the common pitfalls I managed to avoid.
Reference:
https://www.motorcyclespareparts.eu/suzuki-parts/motorcycles/dl1000-v-strom-2002/clutch-450926.aspx
On the slave cylinder side:
- Don't lose the pin (#28)
- Don't forget to put the spacer (#32) around the left bolt in the proper position. All too easy to get this wrong.
- When installing the slave cylinder, do NOT engage the clutch handle. This puts too much strain on the whole system and the result will be that something is crooked. The lever should be fully disengaged, and before mounting the cylinder, the piston should be pressed into the cylinder as much as possible. Only once the slave cylinder is bolted in place should you pump the lever a few times to make sure everything is engaged properly. (Note that, with the lever disengaged, the weight of the clutch fluid will try to push the piston out of the slave cylinder. Make sure you put a tie-wrap or something over the slave cylinder assembly to prevent this, while the slave cylinder is off the MC.)
- Clean the pushrod (#21) really well, possibly put a bit of hose over it to protect it from further dirt accumulation.
- Clean the area around the pushrod really well (brake cleaner) and make sure the drain hole is open. Also there's a bit of gasket protruding here, which you can easily cut off. This is a location where a lot of dirt collects, especially if you habitually overgrease the chain, so you may want to clean this area at every service in the future.
- Later model DL1000s received an extra rubber dust cover (#25A, part number 2316602F20) to protect the slave cylinder from dirt. This is an easy and cheap retrofit when you're in there anyway.
On the clutch basket side:
- There is a precise order and orientation in which the clutch plates and friction plates go in. Plus some spacers and whatnot. Read the maintenance manual carefully.
- The last, and only the last, friction plate (#10) is rotated through about 20 degrees (one lug) compared to the others. The gaps between the lugs on the clutch basket (#1) are so that it seems you can put the last two friction plates (#10 and one #11) in, rotated one lug, but that is NOT correct. If you install things this way, the clutch will not engage or disengage ever (forgot which one it was).
- Make sure all sprockets are properly engaged when you put the clutch basket (#1) in. One of the sprockets down there - I think the one to the oil pump - is actually in two halves, spring loaded against each other (to prevent noise/play), and there's a little trick to get the clutch basket sprocket to engage properly.
- The bolts (#5) that hold the disc (#13) in place need to be tightened in a criss-cross star pattern so that everything is tightened evenly.
You may want to look up the video on the Werks basket installation to see all the pitfalls on this side.
The DL1000 has a hydraulic clutch system which self-adjusts when the friction plates wear down - if ever. So by design it cannot simply not slip one day, and slip the next. That leads me to believe that something was installed wrong from the start, but you only started noticing this right now. Or did you maybe put the wrong (car?) oil in it, around the time the plates started slipping?