5150 Head Having a Hissy Fit

[Jazz P Bass]

Can't say about the caps.
I would leave them alone, other than touching up the solder.

To add, V1 should be selected for the least amount of noise.

The other positions are not that picky.

[Pedro Vecino]

Other positions are not that picky, but are also important (V2, V3, V4). It should make the best choice by comparing different units.
Philips 5751 in V1 works great both in quality and in terms of background noise if can accept a slighty lower gain.