I’m a similar level to you and I have items stretching all the way back to level 3.
I keep getting my days mixed up and it’s so annoying! i.e Is tenth day ‘tooka’, ‘touka’ or ‘tokka’. Then there’s the fourth day and eighth day! yokka, youka, yokka? Just starting to get to grips with them! I eat 'you’gurt on the eighth day!
I must have got cow and noon mixed up about twenty times as well!
This is definitely my future, I know those counters are never going to disappear for me. It’s nice to know that one of the WK Greats is a human just like us. 
I remember a trick for these that someone posted. The cow 牛 is a bull and has a horn sticking out the top while noon 午 doesn’t.
My mix ups are 夫 失 矢.
努力 from level 11 probably annoys me the most. I keep thinking it’s どうりょく. I fail the enlighten review every time if I get that far.
I thankfully don’t have actual leeches yet, but I do fail stuff I didn’t see for a while, most recent being 夕, oh yeah I know that one it’s evening ! then I really wanted it to be がい, because there are guys outside right ? THAT COME OUT AT THE EVENING NO BRAIN IT’S THE YOUTH THAT COMES OUT THE EVENING… thanks brain for mixing up the mnemonic with outside, and just the reading itself, appreciate it.
Now talking about Kaniwani… the sheer amount of synonyms are starting to make me want to die, and I guess that’s only going to get worse ?
My biggest shame is getting 先生 wrong so many times… it’s probably one of the words that everyone knew even before studying japanese 
I always forget the radical branch. That’s level 4.
Still, I feel like I’ve got things under control with leeches never above 20. 3 of the current 19 are radicals, and I don’t really care about them. There are always a few typos there as well, as I have no script to prevent that. (my keyboard double or triple registers occasionally)
I just keep WKing my leeches…
Hopefully they’ll go away eventually…
I’m currently level 27, and I have unburned items on every level. And I started WK in Feb. 2017.
Radicals seem to be the worst - I have unburned ones on every level except for 10 and 16. My oldest kanji and vocab are on level 4 (kanji: 仕, 宝; vocab: 先々月, 写す宝, 宝石), but the treasure-related ones shouldn’t count as leeches since they were just added in December.
Yeah, that’s a good trick. Thinking of the protruding top bit as a horn.
矢 失 also massive bugbears of mine!
毛糸 and 羊毛 from level 5 and 6
I don’t understand why, i really dont, but for some reason i type もういと for 毛糸 and ようけ for 羊毛 whenever they reach guru 2
You can remember by “work like a dog” not “work like a doug”. 
Oh nice. I like it. I think I’ll use that.
Of course now I’ll somehow manage to get the mnemonic backwards. 
Who’s to say there aren’t hard-working Dougs out there?
Necro-ing this thread with a week to spare just to say I burned 努力
Complain about your problems everyone! Sometimes that’s all you need to do (also shoutout @Liuyuan couldn’t have done it without you 
).
Well, I have 試す from level 11 at Guru, and 倒 from level 20 at Apprentice among others (I failed it today for the second time… )
All the way back to Level one (Stupid 八つ、and 人工 was a typo I swear)
Ok, so here is mine. 正直. ( しょうじき = honesty)
It’s insane. I always fail the enlightened / burned stage for some reason. Sure the reading is fairly irregular, but still it’s an extremely common word. I have read it or hear it dozen and dozen of time, maybe hundred at this point, and yet when the review come, I get confused. Probably because 正 is strongly associated to せい and 直 to ちょく in my brain so it’s a “double irregular” (of course しょう is not irregular at all, it’s common, but oh well)
I relate to this on a spiritual level. That word gave me an ungodly amount of trouble (and probably still would if I were to resurrect it lol).
My oldest leech at the moment is: 八日 (Lvl 2), for which I just failed the burn the other day for the I-don’t-know-how-manyth time. And I unlocked it in December of 2017…
For some ungodly reason I can’t ever remember if it’s ようか or よっか.
There was good tip for this one - eight days (ようか) are longer than four days (よっか) 
All the way back to level 4 for me 
Also just today failed 動労 again. Usually get the meaning wrong. Not this time, though. Actually switched the readings around for no reason. And on mobile, so I couldn’t double check.
I just burned it !!
But I feel almost bad about it, because by talking about it just yesterday I kinda cheated the SRS, I’m fairly sure I will forget it again in a few month 
Edit : next one in the list of tenacious leech is 生地 (level 8), and it’s another double exceptional reading
