I need to take a pill.
Ave Caesar,
The APL1084 can be either a variable 5A low drop regulator or a fixed one,
depending on the marking. If you have an APL1084 it's a variable, if you
have a APL1084-3.3 or APL1084-5 or . . . it's a fixed one.
A suitable replacement is the LT1084 from Linear Technology. It also comes
in both versions, that's the easy part.
The transistor (?) is a whole new ball-game. I really can't give you more on
that without having seen the circuit. So give us more details, maybe (part of) the circuit diagram or a picture (of your dog).
With kind regards,
on1aag.