hmmmm I'm not quite picturing the wobbly thing.
Do you mean he wobbles as he walks?
Is it like this?
When we first took ours in she was in pretty bad shape nutritionally, when she walked her head wobbled like a bobble-head doll because her muscles were so weak from the poor nutritional state she was in.
Do you mean something like what I described?

Ours stopped doing that in less than a year after she got here & started eating the right foods.
If that's what you mean my guess would be that with the right foods the one you have will stop doing it too.
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PHRatz