The big flake left of Ken's Crack . Work your way up the really obvious flake and/or the gap behind it. Worming and squirming inside the gap is possible, but awkward - the inside walls are mostly smooth and dirty. Staying mostly on the outside of the flake is more fun. I bet the awkward stemming chimney was the original route; it would have felt more secure in the days when "the leader must not fall" due to fragile ropes.
The usual Gunks warning applies: the lower the grade, the less comparable to climbs elsewhere. I'd have called this a 5.5. All moves easy, big holds plentiful, but to me 5.1 implies "climbing a ladder", where each hold is near the next and you don't have to shift your hips around. This one is straightforward, but not *that* straightforward.
Arguing about the rating is about the most interesting thing about this climb, unfortunately. It's suitable for toproping by total novices, otherwise it's got little to recommend it.
Also, I'm told by reliable photos that it gets very wet in the spring.
Climbers on The Flake (left) and Ken's Crack (right)
Very obvious flake to the left of Ken's Crack. Only a few feet above the road, just south of the outhouse. Descend the Uberfall Descent route (around the corner to climber's left).
I've never met a "5.1 leader", but if I did I'd warn them away from this one. (Note that the Williams and Swain guidebooks have this as "PG", not "PG13", but I didn't see a "PG" option in the MountainProject menu.) Only a few opportunities for traditional protection along the route, though maybe you could make it safer if you had some Big Bros. Toproping this is the obvious choice.
The flake ends at a balcony ledge just below the top of the formation. After climbing any route on this formation (including the Uberfall descent route), you can walk on to the balcony from climber's left and conveniently stand and build an anchor using cams in a horizontal crack. (The crack is an inch or two wide, maybe; I wasn't paying attention). If you don't have cams, you can run very long slings from trees - the tree above Ken's Crack and another tree about ten feet to climber's left of the Flake, at the entrance to the balcony. (This violates the principle of Redundant / No Extension in a big way, but those trees are bomber.)
Inside -- seemed much harder than 5.1, if done in the obvious way as a chimney on the inside. There's a little section where the chimney gets almost a little inverted, and just then there's no definite footholds. Doable, Yes. Even a bit interesting, if you're into chimney moves. But difficulty more like 5.4, or at least 5.3.
Outside - (as top-rope) - doing it all on the outside (right side) is kind of interesting, difficulty like around 5.4+, with an overhang just off the ground, then another bulge higher up. Would be worthwhile if it were longer. Or think of it as a quick test of "readiness" for that level of difficulty.