Interesting - I had exactly the same issue when I got my late 235 first - same cylinder.
Turned out I needed new hydraulic lifters.
Ah, the recurring mystery and confusion about hydraulic lifters.....
Late 235 blocks are all drilled to use solid OR hydraulic lifters, which look almost identical.
There is no oil supplied through the push rods.
Hydraulics 'pump up' with oil from the block gallery, not from the top, which has little pressure and just enough for the rockers.
I had hydraulics on my daily late 235 for 12 years now and hardly ever have to adjust them.
- Easiest and surest way to adjust hydraulics is at idle with the engine hot.
Tighten until the clicking just disappears and then go 1/8 or 1/4 more turn. As long as the pushrods are spinning - you are in good shape, as that means that the lifters are spinning, which is a very good thing.
The shop manual suggests to tighten them 1-1/2 turns, but that's way too much as it prevents the pushrods from spinning, which means lifter\cam lobe wear - not so good. Let alone your valves never fully close !!!
Before worrying about lifters, check your cam to know if it needs solid or hydraulic lifters first.
235/261 cams have small casting lumps on the rear of the cam, between the 3rd and 2nd to the rearmost cam lobes.
2 or 4 raised "lumps" identify it as a hydraulic cam, 1 or 3 lumps as a mechanical lifter cam.
Also make sure you are at least aware of the lack of zinc in oils sold after 2006.
There is plenty info on this forum and all over the web.
If you break in new lifters, use the same method as breaking in a new cam/lifters. 15 minutes at 2000 rpm should do.
