I have a couple of Lamy 2000s, one inked with Diamine Wild Strawberry and the other one with Sailor Manyo Yamabuki. It takes me a couple of months to write them dry, after which I give them a good cleaning and ink them back up again.

The Diamine Wild Strawberry has been fine, but about a month into my latest fill of the Sailor Manyo Yamabuki it started coming out as a distinctly dark brown. I took the nib and feeder out to give it a scrubbing, and there was a build up of residue on the nib that took some scrubbing to get off. The ink behaved fine for the rest of the day, but has already started to darken again after about 72 hours.

Should I dump what's left in the reservoir? Try a different ink? Or is this normal for Yamabuki?