How can I fix Duravit Stark 3 fill vavle?

Hi all. We have a Duravit Stark 3 toilets which I understand have their own specific type of fill valve. I was trying to fix that classic whistling sound that tells you "please clean the fill valve top." So I went ahead and did so. It no longer whistles as it did, but there is some odd noise, and water is cascading from the top but very little flows through the refill hose. I assume I've somehow inserted the seals incorrectly or they slipped as I was reassembling it, but after multiple tries, I've had no luck.

A few other details: 1. It now makes a grinding noise when it flushes, which is a sound in my experience doing basic work on previous toilets that I am unfamiliar with. 2. After filling essentially all the way, it continues to run in spurts for a few minutes, with just a little trickle in each spurt. It is not the same as if the flap valve were loose, dirty, etc. and the toilet just kept running. Again, this is something I'm unfamiliar. 3. The water pressure coming out of the top seems to vary from flush to flush. For example, at times with the cap off the water doesn't shoot out the top; at other times, if I didn't hold a glass over the top with the cap, I'd cause a second Great Flood. 4. Every other flush, the bowl flushes properly. When it does flush properly, the bowl doesn't fill fully (as suggested in the original post when I mentioned it seemed that there was an inadequate amount of water going through the refill hose). When it doesn't flush properly, the water level in the bowl is higher, but (I think) just because the water doesn't empty from the bowl.

Many thanks in advance for your help!