That's weird, as I said my 1525 was factory built with a T6400 and I've run a T6500 (to test it for a customer's "problem child" HP notebook)
The SLGF4 is a T6500.... "Penryn", but then again so is that T9300 you mention.
I've seen others that were T6500, dell was (and still is) kinda "what's cheap this week?" on what CPU would go into a specific notebook. Not that whatever CPU they were building with was "Substandard" but...
The T8300 is also a "Penryn" (Working great in my 1525...)
I HAVE run into compatibility issues with some memory, certain SIMMs run forever in one notebook but refuse to boot in another, I've found that the best way to swap RAM into dell notebooks is one SIMM at a time, you swap both you get a no-boot
swap one, and then the other and all works fine, and there's no technical reason
it should be so,
Hey, at least the CPU is easy to switch out on a 1525...
Here's an odd suggestion for you...
Swap in the T2370 let it go through it's startup routine,
load "Device driver" for the new CPU, reload the Dell Chipset driver
then go check yo see if you have the latest Bios (should be "A17")
THEN try the T6500 arain.
I've actually got a Dell 1525 here that was originally built with a
T2370 and it's currently running a T8300.
I even ran a T6400 in it for a week, So other than guessing
I really don't know what else to suggest.