Also, one function of the "pad" can be to distribute the pressure more evenly over the (softer) felt. But as Rick suggests, the pads may generally serve as "shims" (i.e., providing some additional "padding" or thickness to achieve exactly the correct alignment). My Mack Brass euph currently has only "felts" (though these are of synthetic material), and no pads/shims. My 1924 tuba has felts and thin shims (since it has more wear and needs the shims to get the alignment correct). Finally, cork is often used in lieu of felt since it is not so water absorbent, though it is also harder. So there are a number of options that a tech (or you) might use.
When I got my Mack Brass euph about 5 years ago, it was just great -- wonderful instrument. But the valve felts and corks were absolute CRAP. They got replaced immediately.
Yes, guides are "horn specific" -- at least generally brand specific. In general, my experience is that all these Jin Bao (or similar) instruments intended to be Yamaha clones are in fact Yamaha clones to the degree that they can use Yamaha springs, felts, etc. My Wessex Eb tuba is a Besson clone, and it -- surprise! -- uses those Besson parts.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)