Oxidation forms on bare bras instruments very quickly, you'll see brown and/or green spots developing. You need to ensure you wipe down the horn after every session. Run a swab through the bore to ensure no moisture remains that may leak out to different parts of the horn. Get a can furniture polish, e.g Lemon pledge. Spray it on a dry cloth and wipe down the all parts of the horn, also get some Q-Tips to clean the small tight areas between the keys. The lemon in the furniture polish will help in cleaning up the brass, the wax actually helps protect the bare brass from moisture. you'll see a big difference in doing this routine maintenance. This is what i use on my bare brass P. Mauriat Tenor.