38 USC 1113 - Presumptions rebuttable

(a) Where there is affirmative evidence to the contrary, or evidence to establish that an intercurrent injury or disease which is a recognized cause of any of the diseases or disabilities within the purview of section 1112, 1116, 1117, or 1118 of this title, has been suffered between the date of separation from service and the onset of any such diseases or disabilities, or the disability is due to the veterans own willful misconduct, service-connection pursuant to section 1112, 1116, or 1118 of this title, or payments of compensation pursuant to section 1117 of this title, will not be in order.
(b) Nothing in section 1112, 1116, 1117, or 1118 of this title, subsection (a) of this section, or section 5 of Public Law 98542 (38 U.S.C. 1154 note ) shall be construed to prevent the granting of service-connection for any disease or disorder otherwise shown by sound judgment to have been incurred in or aggravated by active military, naval, or air service.