just a word, w520 heatsink doesnt fit t520 motherboard, there is an engineered difference in the mounting that makes them incompatible
edit to add:
Figure 1: W520 heatsink, note the orientation of the mounting screws, squared
Figure 2: T520 dGPU heatsink, note the orientation of the mounting screws, very stout
Figure 3: T520 iGPU heatsink, with useless noodle pipe and no rear vent
That said, it appears aliexpress has the T520 dGPU fan. Compared to regular T520 fan, this fan has a larger heatpipe and a functioning rear vent. It will be a substantial and worthwhile upgrade over the factory noodle pipe setup which is really only meant to cool 35W dual core i5s and nothing more.
i cannot tell if the T510 fans are compatible either. they appear to also use noodle pipes. so i think the best bet is to buy the T520 dGPU fan on aliexpress.
Also note that the T530 dGPU fan is not compatible, as it adopts the structure of the W510/20/30 fan. So you definitely need at best the T520 dGPU fan.
https://www.aliexpress.us/item/3256802749117659.html