Each Scar I'll keep for Him — Rubber Tree

The question is to find what thing can yield valuable tears from scars. To mis-sum is a hint. Two things are suspicious, the capital of Him He His, and "His own" in line seven. Jesus has only one scar but "would fall so more";
the rubber tree owner is Jesus.

Each Scar I'll keep for Him ¹
Instead I'll say of Gem
In His long Absence worn
A Costlier one

But every Tear I bore ⁵
Were He to count them o'er
His own would fall so more
I'll mis sum them.

(F.920/J.877)

[1] Scar:: a cut in the rubber tree. I:: a rubber tree. Him:: owner of the tree.
[2] Gem:: something valuable, the secretion to make rubber.
[3] Absence worn:: a wound without care.
[4] Costiler one:: the scar with lavishing secretion.
[5] Tear:: the ooze of the tree; a rip, rend. bore:: accepted.
[7] fall:: to drop; to move downwards, an ambiguous word to disguise the poem's true intention; it can be a praise or complaint.
[8] mis sum:: a hint on rubber that used to erase mistakes; to do a wrong calculation, summary.

INDIA RUBBER TREE . . . The Indians make cuts in the tree, and apply clay cups, (which they easily make themselves) to catch the milk. ─ American Magazine of Useful and Entertaining Knowledge (1839)