Here are the pages from the tech guide. The guides are here on the forum if your watchmaker doesn't have them, but I'm most certain he will and we won't be saying anything he doesn't all ready know.
You can see the 'hour recording stop lever' acts on the 'hour recording wheel' to stop the motion. (It just makes the 'intermediate hour recording wheel' slip on the end of the mainspring arbour. In fact that is a very good point for him to check...if that is not properly oiled, then the lever will never be able to hold the wheel in place...the two things are a fine balance to get right.
You can also see that there is a spring called the 'spring for hour recording wheel stop lever' that acts in the stop lever. The spring has a screw head In the middle of it. This screw is eccentric and adjusts the amount of pressure applied to the lever.
The spring can be adjusted through the calendar plate, which is helpful, I only realised on the last one did.
I would check the intermediate wheel is properly, but not overly, lubricated.
Check that the intermediate spring has been installed properly (it can sometimes not sit correctly against the 'intermediate hour recording wheel stop lever'.
Then assemble the calendar plate back on. Careful not to dislodge anything below.
Then with the balance and pivot fork removed I wind the watch from the stem and check it works correctly in both stopped and starting modes...sometimes install the hand, or a spare hand, or a flag of paper/rodico, just to see what is happening.
The spring can be adjusted now through the calendar plate to see if the correct setting can be found.
Here's the bit on oiling the intermediate wheel...
And this is good too...shows how the spring should sit, on side profile...
Btw...guess who just picked up the full "seiko watch technical guide folder" and as well the seiko "watch parts catalogue". All here on the forum of course, but so nice to have the folders!