Testing a hundred+ reforge attempts using Shadow, Copper, and Bronze runic hammers. I found Copper does have the intensity required to produce 100% Mana-Hit Life Leech, but appears unable to produce a value above 70% (Bronze won't get any higher either). The chart below explains where 70% comes from. The max intensity for Leeches in a single roll is 35, hence two rolls on the same Leech at maximum intensity will produce 70%. In order to reach 100%, three rolls would have to hit for near maximum intensity each; 35-35-30 for example. Imbuing can produce 81% Leech values, so 70% can't be the most attainable via reforging. It would seem that the intensities are capped at 70% instead of the correct value of 100%.
Runic tool usage to reforge should have the following outcomes:
1. Combine to total the allowable maximum attribute cap if the intensity is present
2. Ignore rolls of an attribute that is already at cap (item may not receive maximum number of attributes relative to the tool used if multiple rolls apply to an already capped value).
3. Apply the Maximum number of attributes allowable per runic tool used with the maximum intensity divided among the attributes applied.
What reforging shouldn't do is add random attributes from differently named (prefix/suffix) groups if one name is selected. If no name is selected (this mimics the old behavior of runic crafting) then attributes are chosen completely at random. If two different names are selected, there is a greater chance to apply multiple attributes from two specific groups.
Explained here:
uo.com
Update 3/8/2023:
Yoshi Posts:
2,331
October 2022
“Actually I can explain this.
When you choose a single name there’s a chance it will roll a random property outside of that name,
*mage weapon appears in 2 names (arcane/of wizardry) and elemental appears in only 1 name so you’ve technically got very slightly more chance of rolling mage weap”
*Weapon Leech attributes also appear in multiple categories on the table. Also read that when choosing two names the intensity can be lessened for each roll, making some randomness a built-in difficulty perhaps. Question still remains if the correct max intensities are in practice. (Life, Mana, & Stam Leech 100%)
Update 3/8/2023:
Found some more proof that 100% Leech is possible:
uo.com
I-Imbuing
L=Loot
R=Reforge
| Hit Life Leech | 2 – 93(I) 2-100 (R)(L) (see footnote) |
The link below describes how to attain 100% Mana Leech which would be the same method for Hit life Leech at 100%
uo.com
This chart Shows the possible attributes that can be applied when the one name is selected.

This is the intensity chart. Outlined in red is the requirement to attempt to apply 100% Leech attributes