Get the old finish off. Remove what dents you can (ball and magnet method works very well except for dent's in the smaller tubes, knuckles, etc.). Polish raw brass by hand to the degree that you can. Leave it as raw brass.
You will NOT like the result you get by lacquering it unless (as recommended) you remove ALL the dents and then buff it. If you don't have the experience buffing instruments, you will almost certainly ruin it at that stage. If you're committed to doing it yourself, just strip the finish, polish to your level of ability, and leave it raw brass.
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)