If only thinking of the bathroom, (and maybe you've already seen these!!), consider the Vortex replacement fan. It can be bought in a basic exhaust model, or a intake/exhaust multi-speed model.
http://www.amazon.com/dp/B002N1J5IM/ref=pd_lpo_sbs_dp_ss_1?pf_rd_p=1944687702&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B00APSSPEA&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0KEQQ5P6R46083J4AN18
http://www.amazon.com/Roof-Vent-Vortex-Ugrade-Multi-Speed/dp/B00APSSPEA
We have one of each, one is over 6 yrs old with no problems. One real advantage is that it is not necc to replace the whole vent, no roof work or resealing. If you need a new vent, the Fantastic is "fantastic". But more money and work.
'16 Outdoors Timber Ridge 280RKS
Reese 1700# Trunnion w/ DualCam HP
'03 EXCURSION XLT V10 4.30 Axles