Guanyin,new, old or older ?

Just picked up this 9 " tall, 3 lb 6 1/2 oz bronze Guanyin /Kwan Yin.Base is sealed with a thin piece of sheet bronze, and the piece is weighted- fragments of something rattle around inside when you shake it.
When I tap the base sheet it dings like a drum, further up no ding/echo-the core becomes more solid
There are traces of incised or cast seals on the reverse, either very lightly done or worn away (3rd pic down).
It's one of the more attractive Bodhisattvas I've owned, but my experience with Asian bronzes is rudimentary.
Can anyone out there offer an approximation of the age of this piece and country of origin ?
As always-thank you big !
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